A farmer with his arms folded, standing in a dry paddock with gum trees behind him

Handy tools

Water tank & dam calculator

How much water have you got, and how long will it last? Measure your tank or dam and the water depth to see litres when full, litres now and the days left at your daily use.

What are you measuring?

Round tankPoly, steel or concrete tankSquare tank or troughStraight sides, flat bottomDam or dugoutSloping sides (batters)

Diameter m

Across the inside of the tank.

Height to the overflow m

Water can’t sit above the overflow outlet.

Depth now m

Water depth from the floor (or the deepest point). Leave the example to see a part-full one.

Use per day L

Litres of water you use a day - house, stock and garden together. The example is only a starting number. 0 to skip.

Your estimate

23,091 Lwhen full

15,394 Lin it now

7.7 daysat your daily use

Full volume: 23.1 m³ · 23,091 L
In gallons (full): 6,100 US gal · 5,079 imperial gal
Water now: 15,394 L · 67% full
Room left: 7,697 L
Dam floor (worked out): 0 m × 0 m

Link to these numbers

How we work it out

Round tank: π × radius² × depth. Square tank or trough: length × width × depth.
Dam: the floor is the top size less the batter on both sides; the volume uses the prismoidal formula (top, middle and floor areas).
Days left: litres in it now ÷ the litres you use a day. 1 m³ = 1,000 L; 1 ML = 1,000,000 L.

An estimate for a level, regular shape. Real dams are rarely perfectly square and lose water to evaporation and seepage, and tanks lose some volume below the outlet - so keep a margin, and check your tank maker’s rated capacity. Take care near deep water and never climb into a tank to measure. Nothing you type is stored or sent anywhere. Need other units? Try the farm unit converter.

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