Tank Volume Calculator
Find the capacity of a tank and how much is in it right now. Works for vertical and horizontal cylinders, rectangular tanks, capsules and cone-bottom tanks, and prints a dipstick chart from depth to gallons.
Dipstick chart
| Depth | US gallons | Liters | % full |
|---|
How to calculate tank volume
- Choose the tank shape and units, then enter its inside dimensions. For capsules, the length is the straight middle section, not counting the rounded ends.
- Measure the depth of liquid with a dipstick and enter it, or enter the percent full from a gauge.
- Read the capacity and current contents. Use the dipstick chart to turn any depth reading into gallons, and print it to keep by the tank.
Why a half-height reading isn’t half the gallons
In a vertical tank, depth and volume rise together: half the height is half the volume. In a horizontal cylinder they do not, because the tank is widest in the middle. The first few inches at the bottom hold very little, the middle holds the most, and the top fills slowly again. A 48-inch-diameter tank with 12 inches of fuel is a quarter full by height but only about 20% full by volume. This calculator uses the exact circular-segment formula, so partial readings are accurate for any depth.
The formulas
- Vertical cylinder: π × r² × height.
- Horizontal cylinder (partly full): length × [r² × acos((r − h) / r) − (r − h) × √(2rh − h²)], where h is the liquid depth.
- Rectangular: length × width × depth.
- Capsule: a cylinder plus a sphere made of the two rounded ends; the partly full end volume uses the spherical cap formula π h² (3r − h) / 3.
- Cone bottom: a cone (⅓ π r² h) under a cylinder.
One US gallon is 231 cubic inches (3.785 liters); an imperial gallon is 4.546 liters. Measure the inside of the tank: the walls of plastic and fiberglass tanks can be over half an inch thick.
Common horizontal tank sizes
| Diameter × length | Approx. capacity |
|---|---|
| 27" × 44" × 60" oval heating-oil tank | 275 gal |
| 38" × 72" cylinder | 350 gal |
| 48" × 96" cylinder | 750 gal |
| 64" × 144" cylinder | 2,000 gal |
Oval heating-oil tanks are not true cylinders; for an exact chart use the manufacturer’s table. Propane tanks are only ever filled to about 80% to leave room for expansion.
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Frequently asked questions
Do I measure inside or outside?
Inside dimensions give the true capacity. If you can only measure the outside, subtract twice the wall thickness from the diameter.
How do I measure the liquid depth?
Lower a clean stick or tape to the bottom through the fill opening, pull it out and read the wet mark. Make sure the tank is level.
Why does my tank hold less than its label?
Labels often give the nominal size. Fittings, a sloped bottom or rounded ends that are flatter than a hemisphere can all reduce the real capacity.
Can I use it for propane?
Yes for volume, but propane tanks are filled to about 80% and their gauges show percent of total volume, so enter the gauge reading as percent full.
Is anything sent to a server?
No. Everything is calculated in your browser, and nothing you enter leaves your device.