Tank Volume Calculator

1. Choose the unit you measured in (inches, feet, centimetres or metres) and the tank shape: horizontal cylinder, vertical cylinder or rectangular. The labels change to match.
2. Enter the inside dimensions. A lying cylinder needs length and diameter, a standing cylinder needs diameter and height, and a box needs length, width and height.
3. Optionally enter the liquid depth from a dipstick or sight gauge. Leave it blank to see full capacity.

Tank volume is the amount of space inside a tank, usually stated as its full capacity in gallons or litres. The liquid volume is the part of that space filled at a given depth. Fuel oil, diesel, water, rainwater and chemical tanks are all read this way.

Owners need both numbers. Capacity tells you what the tank can take in one delivery. Liquid volume tells you what is left and when to reorder. Tank charts, also called dipstick or strapping charts, list the liquid volume at each depth for a particular tank.

This page is for storage tanks. For a swimming pool with a sloped floor, use the pool volume calculator, which averages shallow and deep ends. For capsule tanks with rounded ends in centimetres and litres, use the water tank capacity calculator.

The calculator multiplies a cross-section area by a length or height, then converts the cubic volume to US gallons and litres.

1. Standing cylinders and boxes. The cross-section is the same at every height, so liquid volume is the floor area times the liquid depth. Half the depth is exactly half the capacity.
2. Lying cylinders. The wet cross-section is a circular segment: the part of a circle below a straight line at depth h. Its area uses the arccosine term minus a triangle, and the volume is that area times the tank length.
3. Units. Sizes are converted to metres with exact NIST factors (1 in = 0.0254 m, 1 ft = 0.3048 m). One cubic metre is 1,000 litres. NIST Handbook 44 defines the US gallon as 231 cubic inches, which equals 3.785411784 litres.

A horizontal cylinder tank is 4 ft in inside diameter and 6 ft long. A dipstick shows 1 ft of liquid.

Full capacity: pi x 2² x 6 = 75.40 ft³ = 564 US gallons (2,135 L).

Segment area at 1 ft: r = 2, h = 1, so 2² x acos(0.5) - 1 x sqrt(3) = 4.1888 - 1.7321 = 2.4567 ft². Liquid: 2.4567 x 6 = 14.74 ft³ = 110 US gallons (417 L).

Meaning: the tank is at 25 percent of its depth but holds only 19.55 percent of its capacity. At 3 ft (75 percent of the depth) it holds 454 gallons, or 80.45 percent. A standing tank 6 ft wide and 10 ft tall, by contrast, holds 282.7 ft³ or 2,115 gallons, and half its height is exactly half of that.

The formulas are exact for perfect shapes, so most real-world error comes from measurement and tank construction.

Inside Versus Outside Size

Measure inside dimensions. On a steel tank a few millimetres of wall hardly matter, but a thick plastic or concrete wall can remove several percent of the volume if you measure the outside.

End Shape

This tool treats cylinder ends as flat. Tanks with dished, domed or rounded ends hold more than a flat-ended cylinder of the same body length.

Tilt and Sludge

A lying tank that slopes toward one end gives a different dipstick reading at each end. Sediment at the bottom takes up space that the formula counts as liquid.

Units and Rounding

All sizes must use one unit. A switch from inches to feet without re-entering numbers changes the result by a factor of 1,728. The gallons to liters converter helps when a label uses the other system.

A standing tank fills in step with depth. A lying tank does not, because it is narrow at the bottom and top and widest in the middle. The table shows the share of capacity at each share of depth.

So a straight depth ratio overstates a low horizontal tank and understates a high one. The three depth results in the tool give a quick chart for your own tank.

Reading a Fuel or Water Tank

Dip the tank, enter the depth and read the gallons left. Compare with the full capacity to see how much a delivery can add.

Sizing a New Tank

Try different diameters and lengths until the full capacity meets your need. For odd shapes such as spheres and cones, the volume calculator covers more solids.

Planning Transfers and Pumping Time

Divide the gallons to move by the pump rate to estimate time. The same volumes help when mixing a treatment at a set dose per 1,000 litres.

1. Using a Straight Depth Ratio on a Lying Tank

A horizontal tank at 25 percent depth holds 19.55 percent, not 25 percent. Use the segment formula.

2. Entering the Radius as the Diameter

The tool asks for the full diameter. Entering the radius cuts the volume to one quarter.

3. Measuring Outside Dimensions

Outside sizes include the wall and overstate capacity.

4. Mixing US and Imperial Gallons

Results are US gallons of 231 cubic inches. An imperial gallon is about 20 percent larger, so use the litre figure for UK labels.

5. Measuring Depth from the Top

The depth field wants the liquid depth from the bottom. A reading of empty space from the top must be subtracted from the height first.

The calculator is exact for ideal flat-ended cylinders and boxes, so its accuracy depends on how closely your tank matches those shapes.

One cubic foot holds 7.48 US gallons (7.480519). A US gallon is 231 cubic inches and a cubic foot is 1,728 cubic inches.

Find the circular segment area at the liquid depth, r squared x acos((r - h) / r) - (r - h) x sqrt(2rh - h squared), and multiply by the tank length.

At half depth the liquid surface passes through the centre, so the segment is exactly half the circle. Every other depth is non-linear.

About 564 US gallons, or 2,135 litres, when full. At 1 ft of liquid it holds about 110 gallons.

Measure the outside circumference with a tape, divide by pi (3.1416), then subtract twice the wall thickness for the inside diameter.

Not accurately. Oval or obround tanks have flat sides and rounded ends, so use the maker chart for that tank model.

A pool has a sloping floor and is read from the water surface, so pool tools average two depths. A storage tank is read by liquid depth from its lowest point.

Exactly 3.785411784 litres. Divide litres by that number to get US gallons.

Yes, for fuels. Liquids expand as they warm, so the same mass fills slightly more space on a hot day. This tool reports geometric volume only.

No. The calculation runs in your browser. The Save button keeps a result only in this browser.

• NIST Handbook 44, Appendix C: 1 gallon = 231 cubic inches (National Institute of Standards and Technology).
• NIST Guide to the SI, Appendix B.8: factors for units listed alphabetically (National Institute of Standards and Technology).
• Circular Segment: area formula (Wolfram MathWorld).
• Horizontal Cylindrical Segment: volume of a partly filled horizontal cylinder (Wolfram MathWorld).