Sauna Size & Electrical Calculator
Three questions — how many people, indoors or out, and what kind of heat — and you get the room dimensions, heater kilowatts, and the circuit your electrician will ask about.
How many people?
Location
Heater type
Room size
4′ × 4′ × 7′
≈ 112 cu ft · 4 ft of bench (2 seated)
Heater & circuit
3 kW · 120V · 40A breaker
Sized at ~1 kW per 45 cu ft with a 125% continuous-load margin.
Planning numbers, not an installation spec — heater manuals override this, and a licensed electrician makes the final call on wire gauge, GFCI, and code. Outdoor and glass-heavy rooms need the bigger heater; when between sizes, go up.
The rules of thumb behind the numbers
- Bench space: about 2 feet of bench per seated person; lying down takes 6 feet. Benches on two walls make small rooms feel bigger.
- Ceiling height: ~7 feet. Taller wastes heat above your head; much lower and the top bench gets brutal.
- Heater sizing: ~1 kW per 45 cubic feet for a traditional electric heater, plus ~30% for outdoor rooms, poor insulation, or lots of glass.
- Electrical reality: almost every traditional heater above 3 kW wants a dedicated 240V circuit. That electrical run is the most commonly forgotten line item in a home sauna budget — get the electrician quote before you buy the kit.
- Infrared is the exception: small cabins plug into a normal 120V outlet, which is why they win for apartments and rentals. See our upcoming infrared vs traditional comparison for the full tradeoff.