Sauna & hot tub calculators

Heater sizing, electricity cost, room sizing and heat-up time — for home saunas and hot tubs. Put your own numbers in and get an answer, with the working shown.

Sauna Electricity Cost Calculator
What one sauna session costs, and what that adds up to per month and per year.
Hot Tub Electricity Cost Calculator
Split your running cost into keeping it hot, the circulation pump, and reheating.
Hot Tub Heat-Up Time Calculator
How long from cold to ready, and what that one heat-up costs.
Sauna Heater Size Calculator
Draw your sauna room and get the heater kW range that actually suits it.

A wooden bucket and ladle resting on a cedar sauna bench — Sauna cost is mostly about how often you heat it.

Two covered hot tubs on a deck during heavy snowfall — Hot tub cost is mostly about the cover and the weather. Hot Tubs, Olympic Village Inn by Rennett Stowe, CC BY 2.0

Guides

What a home sauna really costs to run
Why the common "kilowatts times hours" estimate is too high, what a session actually costs, and how to cut it.
Is a 120-volt hot tub enough in winter?
A plug-in hot tub heats at a quarter the speed of the same tub on 240 volts. It costs the same to run, but here is when it can't keep up with the cold.
How sauna heater sizing actually works
The 1 kW per cubic metre rule, why glass and stone break it, and how to read a manufacturer's chart without getting caught out.