Plumbing and gas calculators
Free calculators for gas rate, gas pipe sizing, radiator heat output, drainage fall, ventilation and water heating. Use the worked examples to check units and assumptions before applying a result to your revision question.
Gas Rate & Heat Input
Heat input from a timed meter-dial reading.
Open calculatorHead ↔ Pressure
Convert vertical head of water to static pressure.
Open calculatorDrainage Fall & Gradient
Convert a drain run and gradient ratio into fall in millimetres.
Open calculatorGas Pipe Sizing Pre-Check
Load, gas volume and route worksheet before the BS 6891 table lookup.
Open calculatorExpansion Vessel Sizing
Estimate vessel volume from water volume, expansion and pressure range.
Open calculatorHeat Loss & Radiator Size
Estimate room heat loss and the radiator catalogue output to look for.
Open calculatorOpen-Flued Ventilation
Room-vent calculation with an explicit input allowance.
Open calculatorCO/CO₂ Ratio
Calculate the ratio from CO and CO₂ readings.
Open calculatorWater Heat-Up Time
Time to heat a volume of water at a given power.
Open calculatorChoose the calculation that answers your question
Gas rate, pipe sizing and combustion readings
Gas rate uses a measured meter volume and time; pipe sizing starts with the demand along a pipe route. Follow the gas rate worked examples or the gas pipe sizing guide to see which inputs you need. A calculated CO/CO₂ ratio still needs the appliance instructions and the rest of the combustion checks to be interpreted.
Radiator sizing, expansion and cylinder heat-up
A radiator BTU calculation estimates required heat output; it does not select the radiator’s height and width. Cylinder heat-up uses stored-water volume and delivered heat input, while expansion-vessel sizing depends on the system’s volume and pressure range. Use the central heating revision notes to connect these quantities to the system diagram.
Drainage fall and water head
Drainage gradient describes a fall along a pipe; water head describes a vertical height that produces static pressure. They use different relationships. The plumbing science worked examples help you set out the units and check whether a result is plausible.
Training & revision aids — live installations follow the full standard, the manufacturer’s instructions and calibrated instruments.