🛢️ Tank Volume Calculator: Gallons, Liters and Cubic Feet
By Shihab Mia · Updated 2026-07-02
This tank volume calculator works out the capacity of a cylinder or rectangular tank and shows it in US gallons, liters, cubic feet and cubic meters at the same time. The default example, a vertical cylinder with a 1 meter radius and a 2 meter height, holds about 1,659.84 US gallons (6,283.19 liters). Enter your own dimensions in the unit you prefer, and add a fill depth to see how much liquid is in a partly full tank.
What is the Tank Volume Calculator?
A tank volume calculator turns a few tape-measure readings into a real capacity figure you can trust for ordering liquid, sizing a pump, or checking a delivery. The tool supports the three shapes that cover the vast majority of real tanks: a vertical cylinder standing on its end, a horizontal cylinder lying on its side, and a rectangular or cuboid tank. You pick the shape from a dropdown, type in the dimensions, and the capacity is calculated instantly.
The math behind each shape is simple geometry. For a vertical cylinder the volume is pi times the radius squared times the height. For a horizontal cylinder it is the same circular cross section, pi times radius squared, multiplied by the length of the tank. For a rectangular tank the volume is just length times width times height. The trick that trips people up is units, so this cylinder tank volume calculator converts every dimension to meters first, computes the volume in cubic meters, and only then converts the result into gallons, liters and cubic feet. That single internal unit keeps the conversions exact no matter which unit you type in.
Unit conversion is where most manual tank calculations go wrong. One US gallon is 3.785 liters, one cubic meter is 264.172 US gallons or 1,000 liters, and one cubic foot is 28.317 liters. Because the water tank capacity calculator does all of this from a single cubic meter figure, you never have to chain conversions by hand or worry about mixing a radius in inches with a height in feet. Just choose one unit for all of your dimension inputs and read the four capacity figures.
The most useful feature for day to day work is the partial fill tank volume calculation. A tank is rarely completely full, so knowing the volume at a given liquid depth matters for gauging stock, billing, or blending. For a vertical cylinder or a rectangular tank the filled volume is simply proportional to how high the liquid sits, so half the height is half the volume. A horizontal cylinder is the interesting case: because the cross section is a circle lying on its side, the filled area follows a circular segment, so a tank that looks half full by depth is exactly half full only at the centerline, and the relationship between depth and volume is curved rather than straight.
That is why a dedicated horizontal cylinder tank volume formula exists. The filled cross-sectional area is r squared times the inverse cosine of (r minus h) over r, minus (r minus h) times the square root of (2rh minus h squared), where h is the liquid depth and r is the radius. Multiplying that area by the tank length gives the filled volume. This calculator applies that formula automatically and clamps the depth so it can never exceed the tank diameter, so your partial readings stay physically sensible.
Whether you are sizing a water storage cistern, checking a fuel tank volume, planning a chemical dosing tank, or working out how much a rectangular tank holds for an aquarium or a pond, this fuel tank volume calculator gives the same reliable answer. It runs entirely in your browser, needs no sign-up, and recalculates the moment you change any input.
When to use it
- Sizing a water tank or cistern and confirming its capacity in gallons and liters before you buy.
- Working out fuel tank volume for a generator, boat, or farm diesel tank so you order the right amount.
- Gauging how much liquid is left in a partly full horizontal cylinder using the partial fill tank volume result.
- Estimating chemical or dosing tank capacity for water treatment and industrial mixing.
- Calculating a rectangular tank volume for an aquarium, pond liner, or IBC tote.
- Cross-checking a supplier delivery against the true tank capacity so you are not overcharged.
How to use the Tank Volume Calculator
- Choose the tank shape: vertical cylinder, horizontal cylinder, or rectangular.
- Pick the unit (meters, feet, inches, or centimeters) that you will use for every dimension.
- Enter the required dimensions: radius and height for a vertical cylinder, radius and length for a horizontal cylinder, or length, width and depth for a rectangular tank.
- Read the full capacity in US gallons, liters, cubic feet and cubic meters.
- Optionally type a fill depth in the same unit to see the filled volume in gallons and liters, plus the percentage full.
- Use Copy summary to save all the figures for your order or notes.
Formula & method
Worked examples
A vertical cylinder water tank with a 1 meter radius and a 2 meter height (the default example).
- Volume in cubic meters = pi x r^2 x h = 3.14159 x 1^2 x 2 = 6.28319 m3
- US gallons = 6.28319 x 264.172 = 1,659.84 gal
- Liters = 6.28319 x 1000 = 6,283.19 L
- Cubic feet = 6.28319 x 35.3147 = 221.89 cu ft
Result: About 1,659.84 US gallons, 6,283.19 liters, or 221.89 cubic feet.
A horizontal cylinder fuel tank with a 0.9 meter radius and a 3 meter length, filled to a depth of 0.9 meters (exactly half).
- Full volume = pi x r^2 x L = 3.14159 x 0.81 x 3 = 7.63407 m3 = 2,016.71 gal
- Filled area at h = 0.9 (which equals r): A = r^2 x acos(0) - 0 = 0.81 x (pi / 2) = 1.27235 m2
- Filled volume = A x L = 1.27235 x 3 = 3.81704 m3
- Filled US gallons = 3.81704 x 264.172 = 1,008.35 gal
Result: Full tank about 2,016.71 gallons; at half depth it holds 1,008.35 gallons, exactly 50%.
A rectangular tank measured in feet: length 2 ft, width 1.5 ft, depth 1 ft.
- Convert to meters: 2 ft = 0.6096 m, 1.5 ft = 0.4572 m, 1 ft = 0.3048 m
- Volume = 0.6096 x 0.4572 x 0.3048 = 0.08496 m3
- US gallons = 0.08496 x 264.172 = 22.44 gal
- Liters = 0.08496 x 1000 = 84.95 L
Result: About 22.44 US gallons or 84.95 liters for the full rectangular tank.
Vertical cylinder tank capacity for common sizes (radius x height, full)
| Radius | Height | Cubic meters | US gallons | Liters |
|---|---|---|---|---|
| 0.5 m | 1 m | 0.785 | 207.5 | 785.4 |
| 1 m | 2 m | 6.283 | 1,659.9 | 6,283.2 |
| 1.5 m | 3 m | 21.206 | 5,602.0 | 21,205.8 |
| 2 m | 4 m | 50.265 | 13,279.0 | 50,265.5 |
Handy volume conversion factors used by this tank volume calculator
| From | To | Multiply by |
|---|---|---|
| Cubic meters | US gallons | 264.172 |
| Cubic meters | Liters | 1,000 |
| Cubic meters | Cubic feet | 35.3147 |
| US gallons | Liters | 3.78541 |
| Cubic feet | US gallons | 7.48052 |
Common mistakes to avoid
- Mixing units between dimensions. Entering a radius in inches and a height in feet gives a wildly wrong capacity. Pick one unit for every dimension. This calculator converts them all to meters internally, but only if each input is truly in the unit you selected.
- Using diameter instead of radius. The cylinder formula needs the radius, which is half the diameter. If you measured across the full tank, divide by two before entering it, or you will overstate the capacity by a factor of four.
- Treating a horizontal cylinder like a linear gauge. For a horizontal cylinder tank, liquid depth is not proportional to volume. A tank at one third of its diameter in depth holds much less than one third of its capacity. Use the partial fill tank volume result rather than a straight percentage of depth.
- Forgetting that real tanks have walls and fittings. These formulas give the internal geometric volume. Measure the inside dimensions, not the outside, and remember that dip tubes, heaters, and baffles slightly reduce the usable capacity.
- Confusing US gallons with imperial gallons. This tool reports US gallons (1 US gallon = 3.78541 liters). An imperial gallon is larger at 4.54609 liters, so a UK reading will be about 20% lower in gallons for the same tank.
Glossary
- Vertical cylinder
- A cylindrical tank standing on its circular end, so height runs top to bottom. Volume is pi times radius squared times height.
- Horizontal cylinder
- A cylindrical tank lying on its side, like a propane or fuel tank. Volume is pi times radius squared times length.
- Rectangular tank
- A box-shaped or cuboid tank. Volume is length times width times height (depth).
- Radius
- The distance from the center of a circular cross section to its edge, equal to half the diameter.
- Fill depth
- The height of liquid measured from the bottom of the tank up to the liquid surface.
- Circular segment
- The area of a circle cut off by a straight chord. It describes the liquid cross section in a partly full horizontal cylinder.
- Cubic meter
- The SI unit of volume, equal to 1,000 liters or about 264.172 US gallons.
- Capacity
- The total internal volume a tank can hold, usually expressed in gallons or liters.
Frequently asked questions
How do I calculate the volume of a tank?
For a cylinder tank, multiply pi by the radius squared by the height (vertical) or by the length (horizontal). For a rectangular tank, multiply length by width by depth. Keep all dimensions in the same unit, then convert the result to gallons or liters. This tank volume calculator does every step for you.
How many gallons is my tank?
Find the volume in cubic meters, then multiply by 264.172 to get US gallons. For example, a vertical cylinder with a 1 meter radius and 2 meter height is 6.283 cubic meters, which is about 1,659.84 US gallons.
How do I find the volume of a horizontal cylinder tank?
A full horizontal cylinder is pi times radius squared times length. For a partly full tank, use the circular segment area A = r squared times acos((r - h) / r) minus (r - h) times the square root of (2rh minus h squared), then multiply by the length. The horizontal cylinder tank volume option handles this automatically.
How do I calculate a partial fill tank volume?
Enter a fill depth in the same unit as your dimensions. For a vertical cylinder or rectangular tank the volume scales with depth over height. For a horizontal cylinder the tool applies the circular segment formula so the partial fill tank volume is exact, not just a straight percentage of depth.
What is the formula for a rectangular tank volume?
Rectangular tank volume is length times width times depth. If the tank is 2 feet by 1.5 feet by 1 foot, that is about 0.085 cubic meters, or roughly 22.44 US gallons.
Does the calculator use US gallons or imperial gallons?
It reports US gallons, where one US gallon equals 3.78541 liters. An imperial (UK) gallon is larger at 4.54609 liters, so if you need imperial gallons, divide the liter figure by 4.54609.
What units can I enter for tank dimensions?
You can enter meters, feet, inches, or centimeters. Choose one unit and use it for every dimension. The tool converts everything to meters first, so the capacity in gallons and liters is accurate whatever unit you start with.
Can I use this as a water tank capacity calculator?
Yes. Water fills the full internal volume, so the water tank capacity calculator result in liters or gallons is the same as the geometric volume. Just measure the inside dimensions of your tank.
Why is my measured depth not half the volume in a horizontal tank?
Because the cross section is a circle on its side. Near the top and bottom, a small change in depth adds or removes only a thin sliver of liquid, while near the middle it adds much more. Only the exact centerline depth corresponds to 50% of the volume.
Do I need to subtract for tank walls and fittings?
These formulas give the internal geometric volume, so measure the inside dimensions. Internal parts like heaters, dip tubes, or baffles take up a little space, so the real usable capacity is slightly less than the calculated figure.