EstimatorKitFree tank volume calculator
Tank capacity, and what the stick reading means
Give the inside dimensions of a tank and the wetted length of a dipstick, and this returns what is in it, what percentage that is, and how much room is left — in US gallons, imperial gallons and liters. Six containers are covered, including the awkward one: a cylinder lying on its side, where the wetted cross-section is a circular segment and a depth gauge that behaves linearly is wrong everywhere except the exact half. A strapping chart for your own tank is generated underneath, ready to print and tape inside the hatch.
- 100% free
- No signup
- 6 tank shapes
- Dipstick chart
- US, imperial and liters
Flat ends, lying down: a fuel tank on a stand, a towable water trailer, a compressor receiver. This is the shape a stick reading lies about.
Inside faces, not the shell. Steel plate, a poly wall and a layer of foam insulation all sit outside the liquid, and on a small tank they are worth several gallons.
In there right now
258 US gal
34.3% full — room for another 494 gal before it is level with the top.
- Holds, brim full
- 752 US gal
- Imperial gallons
- 626
- Liters
- 2,847
- Cubic feet
- 101
- Cubic meters
- 2.85
- Full of water, weighs
- 6,272 lb
Weight uses 8.34 lb per gallon — water at 60 °F, 62.4 lb per cubic foot over 7.48 gallons. Diesel runs nearer 7.1 and a brine nearer 10, so scale it if the contents are not water. It is the figure that decides whether the stand under the tank is adequate.
The segment, worked through
r = 24 in h = 18 in A = r² · arccos((r − h) ÷ r) − (r − h) · √(2rh − h²) A = 576 × 1.31812 − 6 × 23.2 A = 620 sq in V = A × 96 in V = 59,502 cu in = 258 gal
The arccos comes out in radians. Read a quarter of the depth as a quarter of the contents instead and you are five and a half points out: a cylinder on its side filled to a quarter of its diameter is 19.5% full, not 25%.
Dipstick chart — cylinder on its side, 752 US gal full
Every 2 in of wet stick, measured from the inside floor
| Reading | US gallons | Liters | Full |
|---|---|---|---|
| 2 in | 10.7 | 40.6 | 1.43% |
| 4 in | 29.9 | 113 | 3.98% |
| 6 in | 54.3 | 205 | 7.21% |
| 8 in | 82.4 | 312 | 11% |
| 10 in | 114 | 430 | 15.1% |
| 12 in | 147 | 557 | 19.6% |
| 14 in | 182 | 691 | 24.3% |
| 16 in | 219 | 831 | 29.2% |
| 18 in | 258 | 975 | 34.3% |
| 20 in | 297 | 1,123 | 39.4% |
| 22 in | 336 | 1,273 | 44.7% |
| 24 in | 376 | 1,423 | 50% |
| 26 in | 416 | 1,574 | 55.3% |
| 28 in | 455 | 1,724 | 60.6% |
| 30 in | 494 | 1,872 | 65.7% |
| 32 in | 533 | 2,016 | 70.8% |
| 34 in | 570 | 2,156 | 75.7% |
| 36 in | 605 | 2,290 | 80.4% |
| 38 in | 639 | 2,417 | 84.9% |
| 40 in | 670 | 2,535 | 89% |
| 42 in | 698 | 2,641 | 92.8% |
| 44 in | 722 | 2,733 | 96% |
| 46 in | 741 | 2,806 | 98.6% |
| 48 in | 752 | 2,847 | 100% |
How to work out what is in a tank
Three steps, and the middle one is the only measurement a tank without a sight glass will give you.
Choose the container and measure it inside
Six shapes cover what is actually bolted down in a yard or standing in a basement. Every dimension asked for is an inside face: shell plate, a molded poly wall and a jacket of foam insulation all sit outside the liquid, and on a 48 in tank a quarter-inch wall taken by mistake from the outside adds 2.1% — sixteen gallons of tank that is not there.
Drop a stick and type how much of it came up wet
Push a clean rod down until it touches the floor, withdraw it and measure the wetted length. That reading is the only honest input for a tank with no sight glass, and it is what the calculator converts. Setting it to the full inside depth turns the page into a plain capacity check with no partial fill involved.
Read the gallons, then print the chart for next time
You get what is in there now, the percentage that represents, and the room left before it is level with the top — which is the number you give a delivery driver. Below that is a strapping chart for this exact tank in 1, 2, 3, 4, 6 or 12 in steps, laid out to print on one sheet so it can be taped inside the hatch and read without a phone.
Technical specifications
| Containers | Cylinder on its side, upright cylinder, rectangular box, capsule, obround, cone bottom |
|---|---|
| Partial fill, lying down | Circular segment in closed form: A = r²·arccos((r−h)/r) − (r−h)·√(2rh − h²) |
| Curved ends and obrounds | Two hemispherical caps solved as one sphere, π·h²·(r − h/3); an obround's half-rounds detected on whichever axis is shorter, so a 27 × 44 in oil tank reads correctly |
| Dipstick chart | 20 to 36 rows at a 1, 2, 3, 4, 6 or 12 in step, styled to print on one sheet |
| Quarter of the depth | 19.55% of a horizontal cylinder — the error a linear gauge makes |
| Units | US gallons, imperial gallons at 4.54609 L each, liters, cubic feet and cubic meters |
| Contents weight | 8.34 lb per gallon for water; diesel runs near 7.1 and brine near 10 |
| Stored or sent | Nothing — no readings are logged and no chart is saved anywhere |
Frequently asked questions
How much oil is in a 275 gallon tank when the stick reads 26 inches?
About 162 US gallons in the standard 27 in wide, 44 in high, 60 in long basement tank. That shape is an obround — flat sides with a half-round top and bottom — and it measures 268 gallons filled to the very top, which is why the number stamped on it is nominal rather than a capacity you can order against. The last inch or two also sits below the outlet, so it is in the tank without being available.
My horizontal tank reads half way up. Is it half full?
Yes, exactly — and that is the only reading you can trust your instinct on. A cylinder on its side is symmetrical about its center line, so half the diameter is precisely half the contents. Move away from the middle and it falls apart fast: a quarter of the diameter is 19.55% of the contents, three quarters is 80.45%, and the two inches either side of the center line hold 5.3% of the tank against the 1.4% held by the bottom two.
How do I make a dipstick chart for a tank that has no gauge?
Measure the tank once, generate the chart on this page and mark the rod itself. The table underneath the calculator is built from your own dimensions rather than from a generic model, and prints without the site around it. Two things invalidate a chart afterwards: re-levelling the tank, because a cylinder that slopes end to end no longer reads the same everywhere along its length, and any change to where the stick lands on the floor.
Should I measure the tank inside or outside?
Inside, and the gap is bigger than it feels. Volume follows the square of the diameter, so a quarter-inch shell on a 48 in tank is a 2.1% overstatement — sixteen gallons on a 752 gallon cylinder — and a 2 in foam jacket on the same tank overstates it by 19%. Where you can only reach the outside, take the wall thickness off the diameter twice, once for each side.
Why can a propane tank only be filled to 80 percent?
Because liquid propane expands with temperature and the vapor space above it is what absorbs that. The filling limits in NFPA 58 are what fitters work to, and the practical effect is that a 500 gallon domestic tank — 37 in across, 119 in over the domes, so 496 gallons of shell — is full at about 397. Read the capacity figure on this page as the shell, and apply your own fill limit to it.
My tank has a cone bottom. Why does the stick barely move at the start?
Because volume in a cone goes with the cube of the depth, not with the depth. Fill a cone to half its height and it holds an eighth of what the whole cone does, so the first inches off the apex are almost nothing while the last inches before the straight side are worth eight times as much. On the 36 in tank the page opens with, the entire 18 in cone holds 26 gallons against 212 in the barrel above it.
About the segment problem, and why tank pages get it wrong
Standing a vessel up makes depth and contents proportional and there is nothing left to calculate. Lay the same vessel down and the relationship breaks: the wetted end of the tank is a circular segment, its area is r²·arccos((r−h)/r) − (r−h)·√(2rh − h²), and no amount of ratio work reproduces it. The consequences are not subtle. At a quarter of the diameter a horizontal cylinder is 19.55% full, not 25%, so a gauge that reports depth as a percentage is five and a half points optimistic at the point you most want it to be right. The web is full of tank pages that duck this — some accept only a full tank, some interpolate a coarse lookup table, and some show a fill slider whose arithmetic is quietly linear. This one prints the formula with your own numbers substituted into it, because a result you cannot check by hand is not much better than a guess.
The trade’s own answer to the same problem is a strapping table: a calibration chart, one line per inch of depth, produced when the vessel is commissioned and kept with it for the rest of its life. That is what the chart below the calculator is, built from your dimensions instead of from a manufacturer’s model. Two things quietly break one. The first is that every dimension has to be an internal one — a shell, insulation and a coating all sit outside the liquid, and squaring the diameter magnifies the mistake, so a 2 in foam jacket read as part of a 48 in tank overstates it by 19%. The second is anything inside: a baffle, an immersion heater, a heating coil or a dip tube occupies gallons the geometry cannot see, and has to be subtracted separately. An out-of-level tank is a third, and the cruellest, because the chart carries on looking correct.
One number this page produces is not about liquid at all. A full tank of water weighs 8.34 lb a gallon, so the 752 gallon cylinder it opens with is more than three tons standing on whatever is underneath it — which is a footing question, and the concrete slab calculator sizes the pad and the secondary containment wall that most fuel installations need around them at 110% of the largest tank. If what you have is round but solid, or a pipe wall rather than a vessel, the cylinder volume calculator is the shorter route, and a basin with a sloping floor rather than a welded shell is the pool volume calculator.
The stick reading stays on the stick
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — measurements, quantities, the prices your supplier quoted you — is uploaded, logged or kept, which is also why the calculators carry on working on a site with no signal.
The strapping chart is generated in the page each time you change a dimension and is never stored, which is also why printing it is the way to keep one. Nothing about your tank, your levels or your delivery schedule exists anywhere after you close the tab.