Calculator
Hot tub water volume and fill time
Choose round or square, enter the inner size and the water depth in cm or inches, then your hose flow in litres per minute. Time a 10 litre bucket from the garden tap if you do not know it.
In short
Round: litres = pi x (inner diameter cm / 2)² x depth cm / 1,000. Square: litres = length cm x width cm x depth cm / 1,000. One litre of water weighs about 1 kg, a UK gallon is 4.546 litres, and fill time in minutes = litres / hose L/min.
Work out litres and fill time
ShapeUnit
- Water
- 972 L
- 214 UK gallons
- Water weight
- 972 kg
- Base load
- 322 kg/m²
- Fill time
- 1 h 21 min
One litre of water weighs about 1 kg. For the full load on the base, add the weight of the empty tub and the bathers. A typical garden tap gives roughly 10 to 15 litres per minute: time a 10 litre bucket to find yours.
The formulas
| Quantity | Formula |
|---|---|
| Round tub, litres | pi x (inner diameter cm / 2)² x depth cm / 1,000 |
| Square tub, litres | length cm x width cm x depth cm / 1,000 |
| Inches to cm | x 2.54 |
| UK gallons | litres / 4.546 |
| Water weight | 1 litre is about 1 kg |
| Load on the base | total kg / footprint m² |
| Fill time | litres / hose litres per minute |
- Level concrete slab
- Decking: check it is rated for the load
- Compacted, level gravel with a mat