Tank Volume Calculator
Work out the capacity of a tank by shape — vertical or horizontal cylinder, rectangle or capsule. Enter the dimensions and, if you like, the liquid level, and get the full and filled volume in US gallons, liters, cubic feet, cubic meters, imperial gallons and barrels, with the fill percent — plus a by-level table, a units table and a downloadable PDF.
| Level | Filled volume | Fill % | Liters |
|---|---|---|---|
| Enter a tank to compare | |||
| Unit | Full capacity | At this fill |
|---|---|---|
| Enter a tank to compare | ||
How to use the tank volume calculator
Four quick steps turn a tank’s dimensions into its capacity — full and at any liquid level — in US gallons, liters, cubic feet, cubic meters, imperial gallons and barrels, with a by-level table and a downloadable report.
Pick the shape
Vertical or horizontal cylinder, rectangle/box, or capsule with rounded ends.
Enter dimensions
Diameter, height, length or width in inches, feet, centimetres or metres.
Add a liquid level
Optionally enter the fill height or depth to get the partial volume.
Read results & save a PDF
Get the full and filled capacity, fill percent, and every unit — then download a report.
The formulas behind the capacity
Each shape has its own volume formula. The calculator computes the volume in cubic feet, handles partial fills with circular-segment math, then converts to every common unit.
▶ Worked example
An upright round tank is 4 ft across and 5 ft tall. The radius is 2 ft, so the volume is π × 2² × 5 ≈ 62.8 cubic feet.
= 470 US gallons (1,779 L)
That is also about 1.78 m³ or 11.2 barrels. Filled to 4 ft, it holds 80% of capacity — roughly 376 gallons — because an upright cylinder fills in direct proportion to its height.
Tank volume quick reference
The volume formula for each shape, what a cubic foot converts to, and the full capacity of common round tank sizes.
| Shape | Full-volume formula | Partial fill |
|---|---|---|
| Vertical cylinder | π × r² × height | Proportional to height |
| Horizontal cylinder | π × r² × length | Circular segment × length |
| Rectangle / box | length × width × height | Proportional to height |
| Capsule | π × r² × length + 4/3 π r³ | Segment + spherical cap |
r is half the diameter. Volume is computed in cubic feet internally, then converted to every unit.
| Measure | Equivalent |
|---|---|
| US gallons | 7.48 gal |
| Liters | 28.32 L |
| Imperial gallons | 6.23 imp gal |
| Cubic meters | 0.0283 m³ |
| Oil barrels (42 gal) | 0.178 bbl |
| Diameter × height | Cubic feet | US gallons | Liters |
|---|---|---|---|
| 2 ft × 4 ft | 12.6 cu ft | 94 gal | 356 L |
| 3 ft × 5 ft | 35.3 cu ft | 264 gal | 1,001 L |
| 4 ft × 5 ft | 62.8 cu ft | 470 gal | 1,779 L |
| 5 ft × 6 ft | 117.8 cu ft | 881 gal | 3,336 L |
| 6 ft × 8 ft | 226.2 cu ft | 1,692 gal | 6,405 L |
| 8 ft × 10 ft | 502.7 cu ft | 3,760 gal | 14,233 L |
Full capacity using inside dimensions. Enter your own figures above for an exact result in any shape or unit.
Everything the calculator gives you
One set of dimensions produces a full capacity profile, not just a single number.
Tank volume reference numbers
Built for anyone sizing a tank
Homeowners, growers, and trades all need to turn a tank’s dimensions into a real capacity.
Working out how much a water, heating-oil or rainwater tank holds, or how much is left at the current level before a top-up or delivery.
- Size a rainwater or storage tank for the roof area
- Read the gallons left from the dipped fill level
- Check a delivery against the tank’s true capacity
Sizing irrigation, stock-water and chemical tanks — often horizontal cylinders where a partial fill isn’t a simple fraction of the total.
- Get the true volume of a tank lying on its side
- Mix chemicals to the right ratio for the water held
- Plan trough and supply volumes for the herd
Specifying, ordering or installing tanks — pumps, propane, fuel, process vessels — where capacity in several units has to be right.
- Convert one capacity to gallons, liters, m³ and barrels
- Match a capsule or cylinder to the tank’s real ends
- Hand a client a clean PDF of the figures
Get an accurate capacity
Small habits make a tank volume estimate far more reliable.
Measure the inside
Capacity is interior space, so use inside dimensions. Measuring the outside overstates the volume.
Match the shape to the ends
Domed ends mean a capsule; flat or lightly dished ends are closer to a plain cylinder.
Measure depth across the diameter
On a tank lying on its side, the fill level is a depth from the bottom of the circle, not a height.
Leave an air gap
Don’t plan to fill to the brim. Many tanks have a safe-fill limit — propane is often about 80%.
Keep units consistent
Enter every dimension in the same unit. Mixing inches and feet is the most common slip.
Check the data plate
For billing, ordering or safety, trust the manufacturer’s rated capacity over a geometric estimate.
Allow for shaped ends
Dished, coned or sloped bottoms, baffles and fittings change the real volume — treat the figure as an estimate.
Frequently asked questions
Common questions about tank capacity, partial fills, and unit conversions.
The volume depends on the tank’s shape. For a rectangular or box tank, multiply length by width by height. For an upright cylinder, multiply the area of the circular base — pi times the radius squared — by the height. The radius is half the diameter.
Work in consistent units, then convert the result to gallons or liters: 1 cubic foot holds about 7.48 US gallons or 28.32 liters.
For example, an upright cylinder 4 feet across and 5 feet tall has a radius of 2 feet, so its volume is pi times 2 squared times 5, which is about 62.8 cubic feet, or roughly 470 US gallons. This calculator handles vertical and horizontal cylinders, boxes and capsules, and converts to every common unit for you.
A tank on its side is harder because a partly filled horizontal cylinder is not a simple fraction of the total. The full volume is the same as any cylinder — pi times the radius squared times the length — but a partial fill needs circular-segment math.
The cross-section of the liquid is a segment of a circle, whose area is r squared times the inverse cosine of (r minus depth) over r, minus (r minus depth) times the square root of (2 times r times depth minus depth squared). Multiply that area by the tank’s length to get the filled volume.
Because of this, a horizontal tank filled to half its diameter is exactly 50 percent full, but at a quarter of the diameter it holds less than a quarter of its capacity. This calculator does the segment math for you, so you just enter the fill depth.
One cubic foot holds about 7.48 US gallons, or 28.32 liters. So to turn a volume in cubic feet into US gallons, multiply by 7.48; for liters, multiply by 28.32.
Other handy conversions: 1 US gallon is 3.785 liters, 1 imperial (UK) gallon is 4.546 liters, and 1 oil barrel is 42 US gallons. A cubic meter is 1,000 liters, or about 264 US gallons.
For example, a 62.8-cubic-foot tank holds 62.8 times 7.48, which is about 470 US gallons, or 62.8 times 28.32, about 1,779 liters. This calculator shows the capacity in US gallons, liters, cubic feet, cubic meters, imperial gallons and barrels at once.
For an upright cylinder or a box, the partial volume is simply proportional to the fill height: fill to half the height and you have half the capacity. Multiply the full volume by the fill height divided by the total height.
For a tank lying on its side, the fill is measured as a depth across the diameter and the math is not linear — it uses the area of a circular segment, so half the diameter is exactly half full, but lower levels hold proportionally less.
Enter the liquid level and this calculator returns the filled volume, the fill percent and the empty space left, using the correct formula for the shape — including the rounded ends on a capsule tank.
Both are horizontal cylinders, but a capsule has domed (hemispherical) ends instead of flat ones, so it holds more for the same straight length. A plain horizontal cylinder is just pi times the radius squared times the length.
A capsule adds the volume of two hemispheres — together a full sphere — to the straight section: pi times radius squared times length, plus four-thirds pi times the radius cubed.
Many propane and air-receiver tanks are capsules; many water and fuel tanks are plain cylinders with flat or slightly dished ends. Pick the shape that matches the ends of your tank, and if the ends are only slightly domed, the plain cylinder will be the closer estimate.
An upright round tank 4 feet in diameter and 5 feet tall holds about 470 US gallons, or roughly 1,779 liters, when full. The radius is 2 feet, so the volume is pi times 2 squared times 5, which is about 62.8 cubic feet, and 62.8 times 7.48 is about 470 gallons.
If the same tank is only filled to 4 feet, it holds 80 percent of that — about 376 gallons — because an upright cylinder fills in direct proportion to its height.
Change the diameter, height or fill level in this calculator to get the exact figure for your tank, along with liters, cubic feet and other units.
A calculated figure is a geometric ideal from the dimensions you enter, while a rated capacity on the data plate reflects the real tank. Several things cause the gap.
Most tanks are not filled to the brim — a working or safe-fill capacity leaves an air gap (ullage) for expansion, which is why a propane tank’s usable capacity is often around 80 percent of its geometric volume. Wall thickness means the inside is smaller than the outside, and dished, coned or sloped ends, plus baffles and fittings, take up space this simple-shape math doesn’t account for.
Use the calculator for a planning estimate, but trust the manufacturer’s rated capacity for billing, ordering or safety decisions.
Always use the inside (interior) dimensions. Capacity is about the space available for liquid, so the wall thickness should not be included.
Measuring the outside overstates the volume, and for a small tank with thick walls the difference can be several percent. If you can only reach the outside, subtract twice the wall thickness from each outside dimension to approximate the inside.
This calculator assumes the dimensions you enter are interior measurements. For the most accurate result, measure inside the tank or use the manufacturer’s internal dimensions.
Disclaimer: Capacity uses inside dimensions and assumes an exact geometric shape, so measure the interior, not the outside. Capsule ends are treated as true hemispheres; dished, coned or sloped bottoms, wall thickness, fittings, baffles and air gap (ullage) will change the real volume. 1 cu ft = 7.48 US gallons = 28.32 liters; 1 barrel = 42 US gallons. A planning estimate — confirm the rated capacity on the tank’s data plate before relying on it.