Measure inside diameter or LxW and the water depth (partial fill OK). Gallons = cubic feet x 7.4805.
Use this for steel/plastic stock tanks, concrete troughs, and rectangular waterers when sizing refill rate or days of supply with the water-needs calculator.
Sloped or oval tanks need section geometry beyond this page — approximate with inscribed rectangle/circle carefully.
Round: volume ft3 = pi x (diameter/2)^2 x depth. Rectangular: L x W x depth. Gallons = ft3 x 7.4805.
round: ft³ = π x (D / 2)² x depth
rect: ft³ = L x W x depth
gallons = ft³ x 7.4805
Use inside waterline dimensions. Freeboard above the water is not included when you enter water depth directly.
Round tank 6 ft diameter, 2 ft water: radius 3 → ft³ ≈ 56.55 → ≈ 423 gallons.
Rectangular 8 x 3 x 2 ft → 48 ft³ → ≈ 359 gallons.
Assumptions: vertical walls; flat bottom; depth is liquid height.
Limits: corrugated or bowl-shaped bottoms change volume slightly.
Responsibility: planning aid — verify with fill meter when dosing medication or hauling water.
Divide inches by 12 before entry (e.g., 24 in = 2 ft).
This page uses U.S. gallons (x 7.4805 from ft3). UK gallon is larger.
Pair gallons here with the livestock water needs calculator.
Enter the actual water depth, not the tank wall height.