Sauna heater sizing calculator
A sauna heater needs 1 kW for every 45 cubic feet of room: a 6 by 6 by 7 foot room (252 cubic feet) needs 5.6 kW, or 7.0 kW if its walls include concrete, tile or glass.
The standard sizing rule for traditional sauna heaters is 1 kW of heater power per 45 cubic feet of room volume. Rooms whose walls include concrete, tile, or glass need about 25 percent more, because those surfaces absorb heat. The calculator below handles your exact dimensions; a reference table of common room sizes follows it.
Your heater power
- Room volume
- 252 cu ft
- Recommended heater power
- 5.6 kW
Compare heater power across the full sauna database, then confirm the final sizing with the heater manufacturer's own chart; models vary.
Common room sizes at a glance
| Room (L x W x H) | Volume | Heater power | With concrete or glass walls |
|---|---|---|---|
| 4 x 4 x 7 ft | 112 cu ft | 2.5 kW | 3.1 kW |
| 4 x 6 x 7 ft | 168 cu ft | 3.7 kW | 4.7 kW |
| 5 x 7 x 7 ft | 245 cu ft | 5.4 kW | 6.8 kW |
| 6 x 6 x 7 ft | 252 cu ft | 5.6 kW | 7.0 kW |
| 6 x 8 x 7 ft | 336 cu ft | 7.5 kW | 9.3 kW |
| 8 x 8 x 7 ft | 448 cu ft | 10.0 kW | 12.4 kW |
Sauna heater size chart
Heater power by room volume at 1 kW per 45 cubic feet, with the 25 percent allowance for concrete, tile or glass walls.
| Room volume | Heater power | With concrete, tile or glass walls |
|---|---|---|
| 100 cu ft | 2.2 kW | 2.8 kW |
| 150 cu ft | 3.3 kW | 4.2 kW |
| 200 cu ft | 4.4 kW | 5.6 kW |
| 250 cu ft | 5.6 kW | 6.9 kW |
| 300 cu ft | 6.7 kW | 8.3 kW |
| 350 cu ft | 7.8 kW | 9.7 kW |
| 400 cu ft | 8.9 kW | 11.1 kW |
| 450 cu ft | 10.0 kW | 12.5 kW |
| 500 cu ft | 11.1 kW | 13.9 kW |
Heater sizing questions
- What size heater does my room need?
- One kW of heater power for every 45 cubic feet of room volume. A 6 by 6 by 7 foot room is 252 cubic feet, which comes out at 5.6 kW, so the nearest size sold is 6 kW. Enter your own dimensions above for the exact figure.
- Do concrete, tile or glass walls change the answer?
- Yes, by about 25 percent. Those surfaces absorb heat instead of holding it in the room, so the same 252 cubic foot room with a glass front works out at 7.0 kW rather than 5.6 kW. The checkbox in the calculator applies exactly that factor.
- How much does ceiling height matter?
- It is one of the three dimensions in the volume, so it counts fully. On a 6 by 6 foot footprint every extra foot of ceiling adds 36 cubic feet, which is another 0.8 kW of heater. That is why the rule is volume rather than floor area.
- What happens if the heater is under the calculated size?
- It has to run longer to reach its set temperature and, in cold weather, may not reach it at all. The rule sizes for the room you measured, not for a preference, and a heater above the figure costs more to buy and more to run without changing the temperature it settles at.
- What comes after the kW figure?
- The circuit. A heater is a continuous load, so code sizes the breaker and the wire at 125 percent of its draw, which puts a 6 kW heater at 240 volts on a 35 amp circuit with 8 AWG copper. The electrical requirements calculator works that out for any heater power.
Prices and specifications verified September 27, 2026, and re-checked weekly after that. How these numbers are checked.
Free guide: sizing and budgeting a home sauna
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