Water tank volume calculator

A water tank volume calculator turns the geometry of a home, garden, or farm storage tank into usable capacity in liters and US gallons, plus the liquid volume sitting at any measured fill depth. Choose rectangular, vertical cylindrical, or horizontal cylindrical shape; enter the matching positive dimensions in metres, centimetres, millimetres, inches, or feet; and supply a non-negative water level from the bottom. The tool converts everything to cubic metres with fixed closed-form formulas, then scales to litres and US liquid gallons so you can size rainwater barrels, verify supplier nameplates, or convert a dipstick reading into remaining capacity.

Formulas for rectangular and cylindrical water tanks

Three shell geometries cover most domestic and light agricultural water tanks. A rectangular (box) tank has capacity equal to length times width times height when all three dimensions use the same length unit; the liquid volume at fill depth h is length times width times h, provided h does not exceed the tank height.

A vertical cylindrical tank—common for above-ground plastic garden tanks and many steel drums standing upright—has capacity π r squared times height, and filled volume π r squared times h, again with h at most the shell height.

A horizontal cylindrical tank, such as a buried cistern or a long farm bullet lying on its side, has the same total capacity π r squared times axial length, but the free surface is a chord of the circular cross-section, so filled volume is length times the classic circular segment area: r squared times arccos of ((r minus h) over r) minus (r minus h) times the square root of (two r h minus h squared).

At h equals zero the tank is empty; at h equals r a horizontal cylinder is half full; at h equals the diameter the shell is full. All dimensions are first converted to metres using the selected unit (one metre, one hundredth of a metre for centimetres, one thousandth for millimetres, zero point zero two five four metres per inch, or zero point three zero four eight metres per foot).

Cubic metres then scale by one thousand to litres and by division by three point seven eight five four one one seven eight four to US liquid gallons. The calculator does not model dished heads, conical bottoms, elliptical ends, or freeboard; those features need extra segment formulas outside this contract. Keep every linear field in one unit system so the cubic product remains physically meaningful before the litre and gallon conversion.

Practical tips, limits, and related searches

Measure internal dimensions when possible; external wall thickness inflates capacity if you feed nameplate outer sizes without correction. For vertical tanks keep fill depth at or below height; for horizontal cylinders keep fill depth at or below the diameter. Zero fill depth is valid and yields zero filled volume with full empty capacity, which is useful for empty-tank inventory scripts.

Prefer metres for engineering take-offs and centimetres or inches when reading a household dipstick; convert mixed unit notes before you call rather than mixing feet of length with inches of depth in one request. When teaching or writing tests, pair a simple rectangular tank at half height with a vertical cylinder full fill and a horizontal cylinder at half diameter so students see linear versus segment volume.

This landing targets people searching for a water tank volume calculator, rainwater tank capacity in liters and gallons, or garden tank fill-depth volume online; it is not an industrial fuel-bullet only tool without litre conversion, not a concrete footing volume estimator, and not a unit converter that ignores tank shape.

Prefer this capability when you already know the shell geometry and a water level and need capacity plus filled volume in consumer liquid units; if your source is an irregular bladder or a tank with conical base, decompose or measure calibrated volume separately. Round-trip checks are easy: a full rectangular or vertical fill should match capacity within floating tolerance, empty fill should yield zero filled liters, and a horizontal half-diameter fill should yield half of total capacity.