Tank Volume Calculator
Calculate the total capacity of a tank and how much liquid is in it from the fill height. Works for horizontal and vertical cylinders, rectangular tanks and capsule tanks with rounded ends, and builds a depth-to-volume chart.
Inside diameter
Measured from the bottom. Leave empty for a full tank.
How to use the Tank Volume Calculator
- Choose the tank shape and the unit you measured in.
- Enter the inside dimensions: diameter and length, or length, width and height.
- Enter the liquid depth measured from the bottom, or leave it empty for a full tank.
- Read the filled volume, fill percentage and total capacity.
- Use the dip chart to convert any stick reading into gallons or liters.
Tank volume formulas
| Tank shape | Total volume | Filled to depth h |
|---|---|---|
| Vertical cylinder | π r² H | π r² h |
| Horizontal cylinder | π r² L | L × [r² acos((r − h)/r) − (r − h)√(2rh − h²)] |
| Rectangular | L × W × H | L × W × h |
| Horizontal capsule | π r² L + 4/3 π r³ | segment area × L + π h² (3r − h)/3 |
| Vertical capsule | π r² L + 4/3 π r³ | bottom cap + cylinder + top cap, by depth |
r is the radius (half the inside diameter), L the length of the straight section and H the full height. Convert the result with 1 US gallon = 231 in³ = 3.785411784 L, 1 ft³ = 7.48052 US gal and 1 m³ = 1,000 L.
Horizontal cylinder: depth vs. fill
| Depth (% of diameter) | 10% | 20% | 25% | 30% | 40% | 50% | 60% | 70% | 75% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|---|---|
| % of volume | 5.2% | 14.2% | 19.6% | 25.2% | 37.4% | 50% | 62.6% | 74.8% | 80.4% | 85.8% | 94.8% |
This ratio is the same for every horizontal cylinder, whatever its size, so it is handy for a quick check of a stick reading.
Frequently asked questions
How do I calculate the volume of a horizontal cylindrical tank?
The full volume is π × r² × length. For a partly filled tank, find the area of the liquid's circular segment, A = r² × acos((r − h) ÷ r) − (r − h) × √(2rh − h²), where h is the liquid depth, and multiply it by the length.
Why is a horizontal tank half full at half its height but not at a quarter?
Because the tank is round, each inch of depth holds a different amount: little at the bottom and top, most in the middle. At 25% of the diameter a horizontal cylinder holds only about 19.6% of its volume, and at 75% about 80.4%.
How many gallons are in a cubic foot?
One cubic foot holds 7.48052 US gallons (28.3168 liters). One cubic inch is 0.004329 US gallons, and 231 cubic inches make exactly one US gallon.
How do I measure the liquid depth?
Put a clean stick or tape straight down to the bottom of the tank through the fill opening, pull it out and measure the wet part. For accurate results, use inside dimensions and measure the depth at the center of a horizontal tank.
What is a capsule tank?
A capsule tank is a cylinder with rounded (hemispherical) ends, like many propane tanks. Its volume is the cylinder part π × r² × L plus one full sphere 4/3 × π × r³ for the two ends. Real tanks often have shallower ends, so treat the result as an estimate.
Is the result exact for my oil tank?
It is exact for an ideal shape. Real oil tanks are often oval (obround) or have dished ends and internal fittings, so the manufacturer's tank chart is the most accurate reference when available.