How many gallons are in a square foot of water one foot deep?

A column of water 1 ft x 1 ft x 1 ft deep holds exactly 7.48052 US gallons, since 1 cubic foot converts to 7.48052 gallons. Double the depth to 2 ft and you get roughly 14.96 gallons per square foot — the gallons-per-square-foot figure always equals the depth in feet multiplied by 7.48052.

Does this work for round or irregular pools?

Yes — first convert the shape to an equivalent flat area (for a circle, pi x radius²), then multiply by the average depth. Enter that footprint here for the volume and coverage rate.

How many litres are in a square metre of water?

Litres per square metre always equals the fill depth in metres multiplied by 1,000 — a tank filled 1.2 m deep holds 1,200 litres per square metre of footprint.

Gallons Per Square Foot Calculator — Pool & Tank Fill Volume (Litres)

Gallons Per Square Foot Calculator: Pool, Tank and Container Fill Volume

This calculator works out how much liquid a flat-bottomed container holds — a pool, water tank, raised bed, or aquarium — from its footprint and fill depth, giving both a total volume and a coverage rate (gallons or liters per square foot/metre).

Enter the area directly, or a length and width to have it multiplied for you, then add the fill height. Switch units any time, and add a price per unit of liquid for an instant fill-cost estimate.

How to Use the Gallons Per Square Foot Calculator

Choose whether to enter the area directly or calculate it from length x width.
Enter your area (or length and width) in the unit you measured in.
Enter the fill height/depth in the same unit system.
Switch between metric and imperial at any time — figures convert automatically.
Read off the total volume, the coverage rate per square foot/metre, and the estimated fill cost.

The Math Behind the Conversion

The formula is simple geometry: Volume = Area x Height. Dividing that volume by the footprint area gives the coverage rate — gallons (or liters) per square foot/metre — which for a flat-bottomed container is really just the fill height, re-expressed in volume-per-area terms.

Worked example: a 10 ft x 10 ft footprint (100 ft²) filled 4 ft deep holds 100 x 4 = 400 ft³, and since 1 ft³ = 7.48052 US gallons, that is about 2,992 gallons — 29.9 gallons per square foot. In metric, a 3 m x 3 m footprint (9 m²) filled 1.2 m deep holds 9 x 1.2 = 10.8 m³, i.e. 10,800 liters, or 1,200 liters per square metre.

Pro Tips

At a typical Australian mains rate of around $0.004 per litre, filling a 3 m x 3 m x 1.2 m pool section or tank (10,800 litres) costs roughly $43 in water alone — many councils also apply drought restrictions on pool refills, so check local rules first.

Only use this formula for a flat, uniform-depth bottom — a sloped pool floor or curved tank needs an average depth, not just the shallow or deep-end figure.
If you're solving for fill time, divide the total volume by your hose or pump's flow rate (gallons or liters per minute).