Calculator

Sauna size calculator: steam room, benches and heater output

Enter how many people bathe at once, who the sauna is for and which heater you plan. The calculator shows bench length, room size and heater output, and below we explain every formula and its source.

Short answer

How big should a sauna steam room be?

Allow at least 60 cm of bench per seated person, a bench depth of 50-60 cm and 100-120 cm from the ceiling down to the upper bench. A family of four fits a steam room of about 2.4 × 1.8 m, roughly 9.5 m³. An electric heater needs about 1 kW per cubic metre, corrected for glass and log walls.

How to use the calculator

Number of people. Enter how many usually bathe at the same time, not how many guests come to a party.
Who it is for. For a family the bench is long enough for one person to lie down. For a group everyone sits.
Heater. For an electric heater you get the output in kW, for a wood-burning one the volume to choose the model by.
Walls and glass. Log walls and any glass, stone or tile add to the volume the heater has to heat.

Sauna size calculator

Figures update as you type. Formulas and sources are below.

Recommendation

Upper bench length: 240 cm; one straight bench along a wall
Steam room inner size: 240 × 180 cm; Floor area: 4.3 m²
Volume (2.2 m ceiling): 9.5 m³
Volume for the heater (corrected): 11.2 m³
Electric heater output: ≈ 11.2 kW; Harvia's table fits a 8-9 kW heater for this volume
Heights: 100-120 cm from the ceiling down to the upper bench, lower bench 40-45 cm below it, bench depth 50-60 cm.

These are planning figures. Always check heater output and safety distances in the manual of the exact heater model.

Embed it on your site

You can put this calculator on your own website or blog. Copy the code and keep the source link.

<iframe src="https://www.trimata.lt/en/tools/sauna-size-calculator/" title="Sauna size calculator" width="100%" height="860" style="border:0;max-width:760px" loading="lazy"></iframe>
<p>Calculator: <a href="https://www.trimata.lt/en/sauna-size-calculator/">Trimata</a></p>

Formulas, assumptions and sources

Figure	How it is calculated	Source
Bench length	People × 60 cm, at least 200 cm for a family, never under 120 cm	60 cm: K-Rauta ↗; 200 cm: our assumption
Bench depth	50-60 cm	K-Rauta ↗
Heights	Ceiling about 220 cm, 100-120 cm from the ceiling to the upper bench, lower bench 40-45 cm below it	K-Rauta ↗
Room depth	180 cm: 60 cm bench, 50 cm step and 70 cm of open floor	Our assumption
Bench shape	Straight along one wall up to 300 cm, longer runs turn the corner (L shape)	Our assumption
Volume for the heater	Room volume × 1.5 for log walls, plus 1.2 m³ for every m² of glass, stone or tile	Harvia manual ↗
Electric heater output	About 1 kW per m³ of heater volume; fitting sizes from the Harvia Vega volume ranges: 4.5 kW 3-6 m³, 6 kW 5-8 m³, 8 kW 7-12 m³, 9 kW 8-14 m³	Prisma ↗, Harvia ↗

Makers' corrections differ slightly: some add 1.5 m³ rather than 1.2 m³ for each uninsulated m². So always check the final output against the table of the heater you choose. Wood-burning heaters are rated differently from electric ones, so for them the calculator shows the volume that must fall within the maker's stated range.

Examples

People and use	Bench	Steam room	Electric heater
2, family	200 cm, straight	200 × 180 cm, about 7.9 m³	8-9 kW
4, family	240 cm, straight	240 × 180 cm, about 9.5 m³	8-9 kW
6, group	360 cm, L-shaped	300 × 180 cm, about 11.9 m³	9 kW
8, group	480 cm, L-shaped	300 × 240 cm, about 15.8 m³	about 17.5 kW

All examples assume an insulated steam room with a 1.4 m² glass door. In a log steam room the heater volume grows by half, so a considerably stronger heater is needed.

What the calculator does not cover

Safety distances from the heater to benches, walls and ceiling. Each heater's manual gives them.
Ventilation, which affects how quickly the sauna heats and how the steam feels.
The rounded ceiling of a barrel sauna: its volume is smaller than a rectangular room's.
The changing room, washroom and terrace.

For sauna makers

These are the questions buyers ask most on the phone: how many people fit, which heater, what it costs with extras. A sauna 3D configurator answers them on the product page: the buyer picks the size, benches and heater, and the image and price update at once. Which choices buyers look for is covered in Sauna configurator: 9 choices buyers want before they call, and the service is described on 3D configurator.

You can put this calculator on your own website or blog: the code is below the calculator.

Frequently asked questions

At least 60 cm of bench when seated. For one person to lie down, the upper bench should be about 200 cm long.

About 2.2 m of inner height is enough. What matters most is 100-120 cm between the ceiling and the upper bench. A higher ceiling adds volume, so the heater has to be stronger.

An insulated steam room without large glass fits an 8-9 kW heater, because 10 m³ falls within Harvia's 8 kW (7-12 m³) and 9 kW (8-14 m³) ranges. With a 1.4 m² glass door the heater volume is about 11.7 m³.

Yes. Glass does not hold heat like an insulated wall, so every m² of glass adds about 1.2 m³ to the volume. A large glass window can raise the needed output by several kilowatts.

Yes. Below the calculator there is code you can paste into your site. Keep the source link.

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