Independent water heater research and comparisonExplore the installer directory
Water Heater System GuideFind a Local Pro

Water heater tool

Tankless Sizing Calculator

Estimate required tankless GPM from simultaneous fixtures or a target flow rate and your temperature rise.

Screening estimate only.This worksheet uses only the values you enter. A licensed plumber's sizing, code review, and installation plan are authoritative.

Tankless flow estimate

Estimate required GPM

Choose simultaneous fixtures or enter a target flow rate. The result pairs that demand with your temperature rise.

Demand input method
Required GPM appears here.Change any input to update the estimate.

Source note: ENERGY STAR explains that whole-home tankless models are rated by GPM and lists average fixture flows of 2.5 GPM for a shower or bathtub, 3.3 GPM for a clothes washer, 2.2 GPM for a kitchen or bathroom sink, and 1.3 GPM for a dishwasher.ENERGY STAR tankless source