Home systems
Pool volume and chlorine, a rough heating and cooling estimate, water heater sizing and rainwater harvesting.
Pool Volume Calculator
How many gallons or litres a pool holds, for rectangular, round, oval and kidney pools, with a constant depth, a slope or a flat-slope-flat floor.
Pool Chlorine Calculator
How much chlorine product raises a pool’s free chlorine to your target, from its volume and the available chlorine on the product label.
BTU Calculator
A rough range for the heating or cooling a room needs, in BTU per hour, tons and kilowatts, from its floor area and your own BTU-per-square-foot figures.
Water Heater Sizing Calculator
The first-hour rating a tank needs for your busiest hour, or the power a tankless heater needs.
Rainwater Harvesting Calculator
How much rain a roof collects, and the tank to last a dry spell.
Pipe Volume Calculator
How much water a pipe holds, in gallons or litres, from its inside diameter and length, with the weight of that water.
CFM Calculator
Air changes per hour from a fan’s airflow and the room’s size, or the CFM a fan must move for the air changes you are aiming for.
Flow Rate Calculator
A tap, hose or pump’s flow in gallons or litres a minute from a bucket test, or from the water’s speed in a pipe, and how long it takes to fill something.
Rolling Offset Calculator
The travel and setback of a rolling pipe offset from its rise and roll, for 45, 22½, 60 or 11¼ degree fittings or any other angle.
Well Volume Calculator
How much water is standing in a drilled well, from the casing’s inside diameter, the well depth and the depth to the water.
Pool Pump Run Time Calculator
How many hours a day to run a pool pump for the turnovers you want, or the flow needed for a set run time.
Pool Heat-Up Time Calculator
How long a pool or hot tub heater takes to raise the water to the temperature you want, with the gas or electricity it uses and the cost.
Water Softener Sizing Calculator
The grain capacity a whole-house water softener needs for your household, hardness and iron.
A house's water and air are sized by arithmetic that is easy to get subtly wrong. A pool's volume decides every chemical dose, and a dose depends entirely on the product's strength, which differs several-fold between liquid chlorine and granules. A tankless water heater delivers far less hot water in a cold climate, because the colder the incoming water, the more energy each gallon needs. A roof collects the rain that falls on its footprint, not its sloped surface. These pages do the arithmetic exactly and are plain about their limits: the cooling figure is a rough estimate, not the Manual J calculation that sizes equipment; the product label governs any chemical dose; and nothing here is a code or safety judgement, which stays with local rules and a qualified installer.