Tank Volume Calculator
Find the volume of any tank in gallons or liters. Pick the tank shape, enter its size, and add the liquid depth to see how much is inside.
Tank chart: gallons at each liquid depth
| Liquid depth | Volume | Percent full |
|---|---|---|
| 0 | 0.0 | 0% |
| 4 | 22.4 | 4% |
| 8 | 61.8 | 11% |
| 12 | 110.3 | 19.6% |
| 16 | 164.6 | 29.2% |
| 20 | 222.4 | 39.4% |
| 24 | 282.0 | 50% |
| 28 | 341.6 | 60.6% |
| 32 | 399.4 | 70.8% |
| 36 | 453.8 | 80.4% |
| 40 | 502.2 | 89% |
| 44 | 541.6 | 96% |
| 48 | 564.0 | 100% |
This tank volume calculator finds the total capacity of a tank and the volume of liquid inside it. It works for 9 tank shapes: vertical and horizontal cylinders, rectangular tanks, oval tanks, capsule tanks, spheres and cone bottom tanks.
To find the volume of a tank, enter the tank dimensions in inches, feet, centimeters or meters. The tank calculator shows the result in gallons, liters, cubic feet and more. Add the liquid depth to see how full the tank is and how much space is left.
How to use the tank volume calculator
To calculate tank volume, follow these six steps:
- Pick your tank shape. Choose horizontal for a tank that lies on its side and vertical for one that stands up.
- Enter the tank dimensions. Measure the inside of the tank when you can, since walls take up space.
- Pick a unit for each size. You can mix units, such as a diameter in inches and a length in feet.
- Add the liquid depth if you want the filled volume. Measure from the lowest point inside the tank. You can also drag the water line in the drawing.
- Read the tank capacity, the liquid volume and the percent full. Change the unit to see the result in gallons, liters or cubic feet.
- Open the tank chart to see the gallons at every inch of depth. You can download or print it.
What the tank calculator shows
- Tank capacity: the total volume of the tank when full.
- Liquid volume: how much liquid is in the tank at the depth you entered.
- Percent full: the liquid volume as a share of the total volume.
- Space left: how much more the tank can take before it is full.
- Water weight: what the tank or its contents weigh if the liquid is water.
Tank volume formulas for every tank shape
Every tank volume formula follows one idea. Find the area of the tank's cross-section, then multiply it by the tank's length or height. A cylinder has a circle as its cross-section, a rectangular tank has a rectangle, and an oval tank has an oval.
A partly full tank works the same way. You find the area of the liquid's cross-section instead of the whole shape. For a vertical tank, that is easy. For a horizontal tank, the liquid forms a curved shape, so the formula is longer.
In every formula below, r is the radius (half the diameter), π is about 3.14159, and h is the liquid depth.
How to tell which tank shape you have
Look at the tank from the end and from the side.
- Round end, flat ends: a cylinder tank. If it stands up, it is vertical. If it lies down, it is horizontal.
- Round end, domed ends: a capsule tank. Propane tanks are a common example.
- Oval end: an oval tank. Check whether the sides are flat or curve all the way around.
- Square or rectangular end: a rectangular tank.
- Ball shape: a spherical tank.
- Round tank with a pointed bottom: a cone bottom tank.
If your tank has dished ends that bulge only a little, pick the cylinder. The result will be slightly low, since the ends hold a little extra.
Vertical cylinder tank volume
A vertical cylinder tank stands upright. A cylindrical tank in this orientation is common for water storage tanks, water heaters and chemical tanks.
Example: A tank 48 inches across and 60 inches tall has a radius of 24 inches. π × 24 × 24 × 60 = 108,573 cubic inches. Divide by 231 to get 470 gallons. Filled to 40 inches, it holds 313.3 gallons, or two thirds of its capacity.
In a vertical tank, the liquid volume grows in a straight line with depth. Half the height always means half the volume.
Horizontal cylinder tank volume
A horizontal cylinder tank lies on its side. Fuel tanks, heating oil tanks and truck tanks often have this shape.
The part in square brackets is the area of the liquid's cross-section, called a circular segment. The acos function gives an angle in radians, so use radian mode on a calculator.
Example: A tank 48 inches across and 72 inches long holds π × 24 × 24 × 72 ÷ 231 = 564 gallons. Filled to 18 inches deep, it holds 193.2 gallons. That is only 34% of the tank, even though the liquid reaches 37.5% of the height.
Rectangular tank volume
A rectangular tank has flat sides and square corners. Many water tanks, totes and stock tanks use this shape.
Example: A tank 10 feet long, 8 feet wide and 6 feet tall holds 480 cubic feet. Multiply by 7.48 to get 3,590.6 gallons. Filled to 4 feet, it holds 2,393.8 gallons.
Horizontal oval tank volume
A horizontal oval tank lies on its side and has an oval cross-section. Most oval oil tanks have flat sides and round ends. A few tanks have a true elliptical shape. Pick the right oval type in the calculator.
Example: A common oval heating oil tank is 27 inches wide, 44 inches tall and 60 inches long. With flat sides and round ends, it holds 267.9 gallons. If the same tank were a true ellipse, it would hold only 242.4 gallons. The tank shape matters.
Vertical oval tank volume
A vertical oval tank stands upright and has an oval footprint. Its volume is the oval's area times the height, so the liquid volume grows evenly with depth.
Example: A tank with a 48 by 30 inch oval base and 60 inches of height holds 323.9 gallons. Filled halfway, it holds 161.9 gallons.
Horizontal capsule tank volume
A capsule tank is a cylinder with a half sphere on each end. Propane tanks and many pressure tanks have this shape. In the calculator, the side length is the straight part only.
The two round ends together form one full sphere, which is why the formula adds a sphere's volume.
Example: A tank 41 inches across with a 96-inch straight side holds 704.9 gallons. Filled to 20 inches, it holds 341.1 gallons.
Vertical capsule tank volume
A vertical capsule tank stands up, with a half sphere at the top and bottom. Its total volume uses the same formula as the horizontal capsule.
The liquid volume depends on where the liquid level is:
- Below the top of the bottom dome: π × h² × (3r − h) ÷ 3
- In the straight part: 2/3 × π × r³ + π × r² × (h − r)
- In the top dome: the full bottom dome and straight part, plus the filled part of the top dome
Example: A tank 36 inches across with a 60-inch straight side holds 370.1 gallons. Filled to 50 inches from the bottom, it holds 193.9 gallons.
Spherical tank volume
A spherical tank is a ball. Water towers and some gas storage tanks use this shape, because a sphere holds the most volume for its surface.
The second formula gives the volume of a spherical cap: the part of a ball below a flat cut.
Example: A sphere 60 inches across holds 489.6 gallons. Filled to 45 inches, it holds 413.1 gallons, which is 84% of the tank.
Cone bottom tank volume
A cone bottom tank is a vertical cylinder with a cone at the bottom. The cone helps the tank drain fully. Water treatment and farm tanks often use this shape.
A cone holds one third of a cylinder with the same base and height. Measure the liquid depth from the tip of the cone.
Example: A tank 48 inches across with a 60-inch straight side and an 18-inch cone holds 517 gallons. Filled to 50 inches from the tip, it holds 297.7 gallons.
| Tank shape | Total volume formula | Liquid volume grows with depth |
|---|---|---|
| π r² H | Evenly | |
| π r² L | Slow, fast, then slow | |
| L × W × H | Evenly | |
| Oval area × L | Slow, fast, then slow | |
| Oval area × H | Evenly | |
| π r² L + 4/3 π r³ | Slow, fast, then slow | |
| π r² L + 4/3 π r³ | Slow at both ends | |
| 4/3 π r³ | Slow, fast, then slow | |
| π r² H + π r² c ÷ 3 | Slow in the cone, then even |
How to calculate gallons in a tank
To figure out the gallons in a tank, find its volume first. Then change that volume to gallons. This works for any tank shape.
- Measure the tank dimensions in inches.
- Use the formula for your tank shape to get cubic inches.
- Divide the cubic inches by 231 to get US gallons.
If you measured in feet, the formula gives cubic feet. Multiply cubic feet by 7.48 to get gallons.
Calculating tank volume by hand: a step-by-step example
Here is the full math for a horizontal tank 48 inches across and 72 inches long, filled to 18 inches. You can follow it on any calculator in radian mode.
- Find the radius: r = 48 ÷ 2 = 24 inches.
- Find r − h: 24 − 18 = 6 inches.
- Find the angle part: acos(6 ÷ 24) = acos(0.25) = 1.3181 radians. Multiply by r²: 576 × 1.3181 = 759.23.
- Find the square root part: √(2 × 24 × 18 − 18²) = √540 = 23.238. Multiply by r − h: 6 × 23.238 = 139.43.
- Subtract: 759.23 − 139.43 = 619.81 square inches. This is the area of the liquid's cross-section.
- Multiply by the length: 619.81 × 72 = 44,626 cubic inches.
- Divide by 231: 44,626 ÷ 231 = 193.2 gallons.
The tank calculator gives the same 193.2 gallons in one step.
Tank dimensions to gallons
Example: A rectangular tank measures 4 feet by 2 feet by 2 feet. 4 × 2 × 2 = 16 cubic feet. 16 × 7.48 = 119.7 gallons.
For more unit changes, use the gallon converter.
Tank volume in liters
To get the tank volume in liters, measure in centimeters or meters.
Example: A vertical cylinder tank 1.2 meters across and 1.5 meters tall has a radius of 0.6 meters. π × 0.6 × 0.6 × 1.5 = 1.696 cubic meters, or 1,696 liters.
The tank volume calculator shows liters for any input unit. Pick "liters" in the result unit list.
Gallons per inch of tank depth
For a vertical tank, every inch of depth holds the same amount. Knowing that number makes it easy to read the tank's level.
Example: A round tank 48 inches across holds π × 24 × 24 ÷ 231 = 7.83 gallons per inch of depth. If the water is 40 inches deep, the tank holds about 313 gallons.
A horizontal tank does not have a fixed gallons per inch. Use the tank chart for those.
How to measure a tank
Good results start with good measurements. A small error in the diameter grows fast, because the formula squares it.
- Measure inside when you can. Outside sizes include the walls. A steel tank wall is thin, but a plastic or concrete tank wall can be an inch or more.
- Find the diameter from the distance around. Wrap a tape around the tank to get its circumference, then divide by 3.14159. A tank 150.8 inches around is 48 inches across.
- Measure the length of the straight part. For capsule tanks, measure the straight side only. The calculator adds the round ends.
- Measure liquid depth with a stick. Lower a clean stick or a tank gauge stick to the bottom. Read the wet mark. For a cone bottom tank, measure from the tip of the cone.
- Use one unit per size. Pick a unit for each field in the calculator. It changes them all to the same unit for you.
- Check the label. Many tanks show their rated capacity on a plate or sticker. Compare it with your result.
Partially filled tank volume
In a vertical tank with straight sides, the liquid volume grows evenly with depth. A tank filled to half its height is half full.
A horizontal tank is different. It is narrow at the bottom, widest in the middle and narrow again at the top. The first inches of liquid hold little volume, and the middle inches hold the most. The same is true for a sphere.
Horizontal tank fill level chart
| Liquid depth, % of tank height | Horizontal cylinder tank, % of volume | Spherical tank, % of volume |
|---|---|---|
| 10% | 5.2% | 2.8% |
| 20% | 14.2% | 10.4% |
| 30% | 25.2% | 21.6% |
| 40% | 37.4% | 35.2% |
| 50% | 50% | 50% |
| 60% | 62.6% | 64.8% |
| 70% | 74.8% | 78.4% |
| 80% | 85.8% | 89.6% |
| 90% | 94.8% | 97.2% |
| 100% | 100% | 100% |
At 10% of its height, a horizontal tank holds only about 5% of its volume. At 90% of its height, it holds about 95%.
Finding the tank level for a set volume
Sometimes you need the reverse: how deep the liquid will be for a given volume. For a vertical tank, divide the volume by the gallons per inch. For a horizontal tank, there is no simple formula.
Use the tank chart instead. Find the volume you need in the chart, then read the depth next to it. A smaller step gives a closer answer.
Example: In the 48 by 72 inch horizontal tank, 282 gallons is half full. The chart shows that level at 24 inches.
How to read a tank chart
A tank chart, also called a dipstick chart or strapping chart, lists the volume at each depth. You measure the depth with a stick, then look up the gallons in the chart.
Our tank calculator makes a tank chart for any shape and size. Open Tank chart under the calculator, pick a step, and download or print it. Tape the printed chart near the tank for quick readings.
Tank capacity vs tank volume
Tank volume is the total space inside a tank, found from its dimensions. Tank capacity often means the amount of liquid the tank can hold in practice. The two numbers can differ.
- Nominal size. Makers often name a tank by a round number. An oval oil tank sold as 275 gallons holds about 268 gallons by its measured size.
- Fill limit. Many tanks are never filled to the very top. A gap at the top, called headspace, leaves room for the liquid to expand.
- Fittings and baffles. Pipes, floats and inside walls take up some space.
- Unusable bottom. An outlet above the floor of the tank leaves some liquid that cannot drain.
The tank volume calculator gives the full geometric volume. For the rated or safe fill capacity, check the tank's label or ask the tank maker.
Water tank volume and size
A water tank volume calculator works the same way for any tank that holds water. Pick the shape, enter the size, and read the gallons. The results above also show the water weight.
Water tank weight
Water weighs about 8.34 pounds per gallon. A full tank can weigh much more than people expect.
Example: A full vertical tank of 470 gallons holds about 3,920 pounds of water. That is close to 2 tons, before you add the tank itself.
Check that the floor, stand or pad can carry the full weight. The tank maker can tell you what base the tank needs.
How long a water tank lasts
To see how many days a tank lasts, divide its volume by the water you use each day.
Example: A 470-gallon tank used at 50 gallons a day lasts about 9.4 days. At 75 gallons a day, it lasts about 6.3 days.
Track your own use for a week to get a real daily number. Use the liquid volume, not the full capacity, if the tank is not full.
Water tank size calculator for rain barrels and storage
To pick a water tank size, start from how much water you need to store. Then use the tank size calculator to find dimensions that hold that volume.
For rainwater, one inch of rain on one square foot of roof gives about 0.623 gallons.
Example: One inch of rain on a 1,000 square foot roof gives about 623 gallons. A 470-gallon tank would fill and overflow.
| Tank diameter | Gallons per foot | Gallons per inch | Liters per foot | Action |
|---|---|---|---|---|
| 2 ft | 23.5 | 1.96 | 89 | |
| 3 ft | 52.9 | 4.41 | 200.2 | |
| 4 ft | 94 | 7.83 | 355.8 | |
| 5 ft | 146.9 | 12.24 | 556 | |
| 6 ft | 211.5 | 17.63 | 800.6 | |
| 8 ft | 376 | 31.33 | 1,423.4 | |
| 10 ft | 587.5 | 48.96 | 2,224 | |
| 12 ft | 846 | 70.5 | 3,202.6 |
Multiply the gallons per foot by the tank height in feet to get the tank's capacity. A 6-foot tank 5 feet tall holds about 1,057 gallons.
Fuel tank capacity
A fuel tank volume calculator helps with heating oil tanks, diesel tanks and farm fuel tanks. These tanks are usually horizontal cylinders, oval tanks or rectangular tanks. Pick the shape, enter the tank dimensions, and add the fuel depth from a gauge stick.
Heating oil and diesel tank volume
Most indoor heating oil tanks are oval with flat sides. Outdoor fuel tanks are often horizontal cylinders. Because these tanks lie on their side, the gallons per inch change with depth. Use the tank chart to turn a stick reading into gallons.
Example: A 27 by 44 by 60 inch oval oil tank holds about 120 gallons when the oil is 20 inches deep.
Propane tank volume
Most propane tanks are horizontal capsule tanks. Pick "Horizontal capsule", enter the diameter, and enter the length of the straight part. The tank calculator gives the full water volume of the tank.
Propane tanks are never filled to their full volume. The supplier sets the fill limit, so ask them how much propane your tank can hold.
Gas tank capacity of a car
A car's gas tank has an irregular shape that fits around other parts. You cannot measure it from the outside. Your owner's manual lists the fuel tank capacity in gallons. If you do not have the manual, the tank size is often listed in the car's specifications from the maker.
You can also estimate the fuel tank size at the pump. Fill the tank when the low fuel light comes on, and note the gallons. The tank holds that amount plus the fuel that was left.
Fuel tank capacity and driving range
Example: A 15-gallon tank in a car that gets 30 miles per gallon gives a range of about 450 miles.
Real range is lower, because no one drives the tank to empty and mileage changes with speed and load.
Common tank sizes in gallons
Use these examples to check your results. Each row loads into the tank calculator.
| Tank | Shape | Size | US gallons | Liters | Action |
|---|---|---|---|---|---|
| 55-gallon drum | Vertical cylinder | 22.5 in × 33.5 in | 57.7 | 218.3 | |
| Round water tank | Vertical cylinder | 48 in × 60 in | 470 | 1,779.2 | |
| Fuel tank | Horizontal cylinder | 48 in × 72 in | 564 | 2,135 | |
| Oval oil tank | Horizontal oval | 27 × 44 × 60 in | 267.9 | 1,014.3 | |
| Capsule tank | Horizontal capsule | 41 in × 96 in side | 704.9 | 2,668.3 | |
| Rectangular water tank | Rectangular | 10 × 8 × 6 ft | 3,590.6 | 13,592.1 | |
| Spherical tank | Sphere | 60 in | 489.6 | 1,853.3 |
A 55-gallon drum holds a little more than 55 gallons when full to the brim. The name is a rounded working size.
Tank volume unit conversions
Tanks can be measured in inches, feet or meters, while storage is quoted in gallons, liters or barrels. Use this unit volume conversion diagram to visualize the relationship between cubic feet and gallons:
| Unit | US gallons | Liters |
|---|---|---|
| 1 cubic inch | 0.004329 | 0.0163871 |
| 1 cubic foot | 7.48052 | 28.3168 |
| 1 cubic yard | 201.974 | 764.555 |
| 1 cubic meter | 264.172 | 1,000 |
| 1 US gallon | 1 | 3.78541 |
| 1 UK gallon | 1.20095 | 4.54609 |
| 1 oil barrel | 42 | 158.987 |
One US gallon is exactly 231 cubic inches. One cubic foot is 1,728 cubic inches, so it holds 1,728 ÷ 231 = 7.48 gallons.
For the UK, Canada and other places that use imperial gallons, pick "UK gallons" in the result unit list.
Tips for calculating tank volume
- Pick the right orientation. A horizontal tank and a vertical tank with the same size hold the same total volume. Their partial fill volumes are very different.
- Use the diameter, not the radius. The calculator asks for the diameter. The formulas use half of it.
- Do not add the round ends twice. For a capsule tank, the side length is the straight part only.
- Check flat sides vs elliptical ends. For an oval tank, the wrong oval type can change the result by about 10%.
- Keep extra digits. Round only the final answer. Rounding the radius first can change a large tank's result by many gallons.
- Compare with the label. If your result is far from the rated size, measure again.
- Measure the depth at the center. On a horizontal tank, take the stick reading in the middle, away from the ends.
- Check that the tank is level. A tilted horizontal tank gives a different depth at each end. Measure at both ends and use the average.
Where tank volume matters
- Water storage. Know how many days of water a tank holds.
- Rainwater harvesting. Size a rain barrel or cistern for your roof.
- Heating oil and diesel. Turn a stick reading into gallons before you order fuel.
- Farms. Size water troughs, stock tanks, sprayer tanks and fertilizer tanks. A round stock tank is a vertical cylinder, and an oval stock tank is a vertical oval.
- Chemicals and dosing. Many water treatment doses are given per gallon of tank volume.
- Moving and installing tanks. Know the full water weight before you choose a base.
For other containers, use the aquarium volume calculator for fish tanks, the pool volume calculator for pools, and the cylinder volume calculator for any round shape.
Related calculators
Frequently asked questions
How do I calculate the volume of a tank?
Multiply the area of the tank's cross-section by its length or height. For a vertical cylinder, that is π × radius² × height. For a rectangular tank, it is length × width × height.
How do I calculate gallons in a tank?
Work out the tank volume in cubic inches, then divide by 231. If you measured in feet, multiply the cubic feet by 7.48.
How do I find the volume of a cylindrical tank?
Use π × r² × length for a horizontal tank and π × r² × height for a vertical tank. The radius r is half the diameter.
How do I calculate the volume of a partially filled horizontal tank?
Find the area of the liquid's cross-section with the circular segment formula, then multiply by the tank length. The tank calculator does this for you when you enter the liquid depth.
What is the difference between tank volume and tank capacity?
Tank volume is the full space inside the tank. Tank capacity is often the usable amount, which can be lower because of headspace, fittings and fill limits.
How many gallons are in a cubic foot?
One cubic foot holds about 7.48 US gallons.
How do I find the diameter of a tank?
Measure the distance around the tank with a tape, then divide by 3.14159.
Does a horizontal tank hold half its volume at half its height?
Yes, at exactly half the height a round horizontal tank is half full. Above and below the middle, the volume does not change evenly with depth.
How do I find the capacity of a fuel tank?
For a heating oil or diesel tank, measure its size and use the tank volume calculator. For a car, check the owner's manual, since car fuel tanks have irregular shapes.
How much does a full water tank weigh?
Multiply the gallons by 8.34 to get pounds of water. A 500-gallon tank of water weighs about 4,170 pounds plus the tank itself.
Can I calculate tank volume in liters?
Yes. Pick liters in the result unit list. You can enter sizes in centimeters or meters too.
Can I use this calculator for a septic tank?
It gives the volume of a septic tank from its size. It does not tell you what size you need. Local health rules set septic tank size, so check with your local authority.
How do I measure the liquid level in a tank?
Lower a clean stick to the bottom of the tank, pull it out and read the wet mark. Enter that depth in the calculator.
What is a tank chart?
A tank chart lists the volume at each liquid depth. You read the depth with a stick and look up the gallons. This calculator makes one for any tank shape.
What size water tank do I need?
Multiply the water you use each day by the number of days you want to store. Then use the tank size calculator to find a tank that holds that volume.
Sources
We checked the formulas and unit values on this page against these sources.
- NIST Handbook 44, Appendix C: General Tables of Units of Measurement. National Institute of Standards and Technology. “Gallon, cubic inch, cubic foot and barrel values.”
- Circular Segment. Wolfram MathWorld. “The area formula for partly filled horizontal tanks.”
- Spherical Cap. Wolfram MathWorld. “The volume formula for partly filled spheres and capsule ends.”
- Water Density. U.S. Geological Survey (USGS). “Water weight per gallon.”
Reviewed by the VolumeCalculator.dev team. Last reviewed: October 29, 2026. How we check our numbers