Home sauna sizes: what internal dimensions do you actually need?

A comfortable two-person home sauna needs roughly 1.2 m × 1.5 m internally; four people need about 1.8 m × 2.0 m; a genuine six needs 2.0 m × 2.4 m or more. Ceiling height should be 1.9–2.1 m — lower heats better and costs less to run. If you want anyone to be able to lie down, one internal dimension has to be at least 2.0 m, and that single requirement drives more sauna layouts than occupancy ever does.

Treat every manufacturer occupancy figure as an upper bound measured with everyone sitting upright and touching. The number that matters is bench length, not the label.

Sizing table

Stated use	Internal footprint	Floor area	Volume at 2.05 m	Bench arrangement	Typical heater
1 person, sitting	1.0 × 1.2 m	1.2 m²	~2.5 m³	One bench, 1.2 m	3–3.5 kW
2 people, sitting	1.2 × 1.5 m	1.8 m²	~3.7 m³	One or two tiers, 1.5 m	4.5 kW
2 people, one lying	1.5 × 2.0 m	3.0 m²	~6.2 m³	Two tiers, 2.0 m upper	6 kW
4 people, sitting	1.8 × 2.0 m	3.6 m²	~7.4 m³	L-shape or two tiers	6–8 kW
4 people, two lying	2.0 × 2.1 m	4.2 m²	~8.6 m³	Two 2.0 m tiers	8 kW
6 people, sitting	2.0 × 2.4 m	4.8 m²	~9.8 m³	L-shape, two tiers	8–9 kW

Internal dimensions, measured wall lining to wall lining. Add 120–200 mm per wall for the external footprint of an insulated cabin, and more for an outdoor build with cladding and a cavity. Heater sizes assume a well-insulated cabin with a glass door — see electrical requirements for how the supply follows from that figure.

Benches: the dimension that actually decides occupancy

Occupancy is a function of linear bench metres, and roughly 500–600 mm of bench length per seated adult is a realistic allowance. A 1.5 m bench seats two comfortably or three at a squeeze. A 2.0 m bench seats three, or one person lying down.

Bench depth matters as much as length:

• 400–450 mm — the practical minimum. Sitting upright, feet down, no leaning back. Common in small cabins and in the specs that generate inflated occupancy claims.
• 550–600 mm — comfortable. You can sit cross-legged, tuck your feet up, or lean back against the wall with a backrest.
• 600–700 mm — required to lie on. Below 600 mm your shoulder or hip overhangs.

Bench length for lying down: about 2.0 m of clear run. Not 1.8 m, not “roughly 2 m including the heater guard”. A 1.9 m person needs 2.0 m of unobstructed bench, and that clear run has to avoid the heater, its guard and the door swing.

Tiers. A traditional sauna is stratified — the air at the ceiling can be 20–30°C hotter than at the floor. That is the entire point of a two-tier layout. A typical arrangement is a lower bench at 450–500 mm above the floor and an upper bench at 1.0–1.15 m, with a footrest so the upper bench is usable without dangling. The upper bench is where the sauna actually happens; a single-tier cabin is a warm room with a bench in it.

The rule that follows: the top bench should sit roughly level with or slightly above the top of the heater stones, and there should be 1.0–1.15 m from the top bench to the ceiling so an adult can sit upright on it. Those two constraints together are what fix the ceiling height.

Ceiling height: why 2.1 m is the ceiling

Internal ceiling height should land between 1.9 m and 2.1 m, with 2.05 m a sensible default.

Going higher is a straightforward waste. Heat rises and stratifies, so any air above head height on the top bench is being heated for nothing — it adds volume the heater must raise, lengthens warm-up and raises the duty cycle at temperature. A cabin at 2.4 m rather than 2.05 m adds about 17% to the volume and a similar amount to every session’s cost, permanently. Our running costs page quantifies what that means in pounds.

Going lower than 1.9 m compresses the bench stack: either the top bench drops below the stones (cool seat, poor löyly) or the headroom on it disappears.

This is one of the reasons converting a garage bay or a tall garden room into a sauna usually involves dropping a ceiling, and one of the reasons a purpose-built cabin performs better than a lined room of the same footprint.

Clearances, door swing and the heater guard

Footprint arithmetic that gets forgotten:

• The heater guard. A wall-mounted electric heater needs manufacturer-specified clearances — commonly 50–150 mm to side walls and 500–1,200 mm above to combustibles — and a timber guard rail in front. Allow roughly 0.3 × 0.5 m of floor area for a wall heater and guard, and 0.6 × 0.6 m for a floor-standing or free-standing stove. A wood-burning stove needs considerably more.
• The door swings outwards. Always, in every sauna, so it can be pushed open in a hurry and never latches shut. That means you need clear space outside the cabin — check it against the garden path, the plant room door or the bathroom layout.
• Door width is typically 600–700 mm with a 1.85–1.95 m height. Sauna doors are deliberately short to keep the hot air in.
• Floor clearance in front of the lower bench: at least 400–500 mm so people can get past each other and stand up without kneecapping someone.
• Ventilation. An inlet low near the heater and an outlet on the opposite wall, usually with an adjustable vent. Neither should be blocked by a bench.

Real usable floor space is therefore the internal footprint minus the benches, minus the heater guard, minus the walking strip. In a 1.8 × 2.0 m cabin, that leaves a floor area of roughly 0.9 m² you can stand in.

Matching the heater to the volume

Once the internal dimensions are fixed, the heater follows from volume, at roughly 1 kW per cubic metre for a properly insulated cabin. Adjust up for:

• Glazing — about 1.2 m³ of notional extra volume per m² of glass.
• Uninsulated or masonry walls — about 1.2–2 m³ per m² of that surface.
• Outdoor exposure in a UK winter, and any solid-stave barrel construction.

So the 1.8 × 2.0 m four-person cabin at 7.4 m³, with a 1.5 m² glass door, prices out at roughly 7.4 + 1.8 ≈ 9.2 m³ of notional volume — an 8 kW heater, and a dedicated 40A circuit. That jump from 6 kW to 8 kW is the point at which the electrical work gets meaningfully more expensive, which is worth knowing before you choose a footprint.

The “6 person” problem

The most common sizing mistake in the UK market is buying to a marketing occupancy figure.

Those figures typically assume every adult sits upright, shoulder to shoulder, on 400 mm-deep benches, on both tiers, with nobody lying down and nobody putting a towel or a drink anywhere. It is a bench-metre calculation, not a comfort calculation. In practice, most home saunas are used by one or two people, and the occasional third.

A workable correction is to halve the stated figure: a “six-person” cabin is a comfortable three, a “four-person” is a comfortable two with room to stretch out. Then check the actual bench length against 500–600 mm per person and 2.0 m for anyone lying down.

Buying to the inflated figure costs you three times over — a bigger cabin, a bigger heater and possibly a heavier circuit up front, then higher running cost for the life of the sauna, then garden space you cannot get back. The are home saunas worth it page makes the same argument from the whole-of-life angle.

Working it out for your space

Start from the space you have, not the occupancy you imagine. Measure the available footprint, subtract the wall build-up, check whether 2.0 m of bench will fit in either direction, and see which row of the table you land on. For an awkward alcove, a chimney breast or a sloping garden, a bespoke sauna is often the only way to use the space properly, and a garden cabin is usually easier to size than an indoor conversion because you are not fighting an existing room.

Our sauna cost calculator takes internal dimensions and returns a heater size and an indicative purchase and running cost, and the fit checker confirms whether the external footprint and height work in the space — including the planning height limits covered on our planning permission page.