Hot Tub & Spa Volume Calculator
Estimate the total water in a round hot tub or spa, in gallons or litres, for chemical dosing.
Imperial / Metric
Calculators
Pools & Water Features
Pool volume, chemical dosing, circulation, heating and covers — plus liners and water storage.
- 16Calculators
- 3Families
- 3Method papers cited
Pool chemistry and hydraulics are both volume problems, and getting the volume right is the part people skip. A pool with a sloping floor, a shallow end and a spa spillover is not a box, and dosing chemicals against a rough volume estimate is how a pool ends up over-treated in one direction and chasing it back in the other.
The chemistry pages here compute a dose from a measured starting point and a target, and they will not tell you what your water currently reads — that requires a test, and a reliable one. Turnover, pump and heater calculations are separate hydraulic problems in which head loss through the plumbing usually matters more than the pump's headline rating.
In-Ground Concrete Pool Shell Volume Calculator
Estimate the concrete (gunite/shotcrete) volume needed for a rectangular in-ground pool shell, distinct from the pool's water-fill volume.
Imperial / Metric
Pool Calcium Hardness Increaser Calculator
How much calcium chloride raises a pool's calcium hardness to your target, at the strength on the label — and why lowering it is a drain, not a dose.
Imperial / Metric
Pool Chlorine Dose Calculator
Work out the chlorine needed to raise free chlorine to a target, for the product you actually have.
Imperial / Metric
Pool Cover & Liner Area Calculator
Work out the cover or liner area for a pool, including the wall wrap a liner needs and the trim a cover does not.
Imperial / Metric
Pool Filter Backwash Water Calculator
How much water a sand filter backwash sends to waste, the rate it washes the bed at, and the salt and stabiliser each backwash throws away.
Imperial / Metric
Pool Heater Sizing Calculator
Estimate the heater output needed to raise a pool to temperature in a target time, and what a cover saves.
Imperial / Metric
Pool Partial Drain and Refill Calculator
How much water to drain and refill to bring stabiliser, salt or calcium down to target, counting your fill water's level, and how far the water line drops.
Imperial / Metric
Pool pH Adjustment Calculator (Acid or Soda Ash)
How much muriatic acid, dry acid or soda ash moves a pool's pH to target, from alkalinity, stabiliser, temperature and TDS, and the alkalinity it leaves.
Imperial / Metric
Pool Pump Turnover Calculator
Find the flow rate and daily run time needed to turn the pool over properly.
Imperial / Metric
Pool Salt Calculator (Salt Chlorine Generator)
How much salt takes a salt-chlorinated pool from its reading to the cell maker's level, by weight and in bags, and how much to drain to come back down.
Imperial / Metric
Pool Stabilizer (Cyanuric Acid) Calculator
How much stabiliser takes cyanuric acid to your target, the free chlorine that level needs, and how much of the pool to drain when it is already too high.
Imperial / Metric
Pool Total Alkalinity Adjustment Calculator
How much bicarbonate or acid moves total alkalinity to where you want it — and why lowering it drags the pH down with it.
Imperial / Metric
Pool Volume Calculator (Rectangular, Round, Oval or Kidney)
The water a rectangular, round, oval or kidney-shaped pool holds over a flat or sloping floor, in litres or US gallons, for dosing and filling it.
Imperial / Metric
Pump Drain Time Calculator
Hours to drain a pool, flooded basement or tank — from the pump's real operating point on its hose, not the zero-head number on the box.
Imperial / Metric
Solar Pool Heater Collector Size Calculator
The solar collector area a pool heater needs as a share of the pool's surface — the US Department of Energy's 50% to 100% rule, by how long you swim.
Imperial / Metric