How Big Does the Sauna Need to Be? Start With the Benches
Last updated: By The SaunaIndex Bench
Floor area is the wrong number to size a sauna by. A 6 by 6 room and a 4 by 9 room have the same 36 square feet and seat completely different numbers of people, because seating is bench run and bench run is a function of which walls you can build against. Put the room in below and this planner lays the benches out, counts the seats and tells you what the room cannot do.
Fit the benches to the room
Verdict
Seats 6, and one bench is long enough to lie on
This room seats 6 at the published 600 mm per person, and its longest bench clears the 1800 mm needed to lie flat.
Bench run
Published bench dimensions
Method
How the layout is worked out
Every step of the geometry is written down here, so you can check the number rather than trust it.
The bench runs along the back wall, and both tiers run its full length. That gives two runs equal to the wall, and seating is the sum of the two divided by 600 mm and rounded down. Six feet of wall is 1,828 mm, which is three whole seats on each tier and six in the room, which is why a modest 6 by 5 footprint handles four people without being tight.
An L-shape adds a return down one side wall, and the arithmetic there is where most plans go wrong. The return cannot start in the corner, because the back-wall bench already fills its own depth there, so the usable return is the room's depth minus that bench's depth. The upper tier loses 600 mm to the corner and the lower tier loses 500 mm, which are the published depths of the two tiers. In a 6 by 7 room that turns a 1,828 mm run into 3,362 mm upstairs and 3,462 mm downstairs, so the room jumps from six seats to ten. What it does not do is make a longer single bench: the back wall is still 1,828 mm and the returns are shorter, so if lying flat matters, the L-shape has bought you nothing at all on that count.
Depth is the constraint people miss until the cedar is ordered. The lower bench sits in front of the upper one rather than under it, so a stepped two-tier bench occupies the upper depth plus the lower depth: 600 plus 500, or 1,100 mm front to back at the published figures. In a 5 ft room that leaves 424 mm of floor, which is a narrow but real standing space. In a 4 ft room it leaves 119 mm, which is nothing. In a 3 ft room the benches simply do not fit, and this planner says so rather than reporting a negative floor as though it were a measurement. The last check is vertical: the room has to clear 1,980 mm before a Harvia electric heater can go in it at all, and that figure is off the manufacturer's own data sheet rather than off a forum.
Sources
The two sources behind every dimension
- Finnmark Sauna, bench sizes and specifications - 600 mm per person, 1,800 mm to lie flat, benches at 1,050 mm and 600 mm, a 300 mm step, upper depth at least 600 mm and lower depth 400 to 500 mm.
- Harvia JH45B electric heater data sheet - minimum sauna room height of 1,980 mm.
Frequently asked questions
What size sauna do I need for four people?
- Four seated people need 2,400 mm of bench at the published 600 mm per person, and that is bench run rather than wall length, so a two-tier bench halves the wall you need. A 6 ft wall gives 1,828 mm on each tier, which is three whole seats per tier and six in total, so a 6 ft by 5 ft room seats four comfortably. The catch is depth rather than width: a stepped upper and lower bench occupies 1,100 mm front to back, so anything shallower than about 4 ft leaves no floor at all.
How long does a bench have to be to lie down on?
- 1,800 mm, or six feet, in one uninterrupted run. That is the figure worth checking before anything else, because it is the one an L-shaped layout quietly fails. Two 1,200 mm benches meeting at a corner add up to 2,400 mm of seating but neither of them is 1,800 mm long, so nobody can lie on either. This planner tests lying down against the longest single bench and never against the total, which is why an L-shape can seat ten people and still report that you cannot lie flat.
How high should the benches be?
- The published layout puts the upper bench at 1,050 mm from the floor, the lower at 600 mm and a step at 300 mm. That spacing is not arbitrary: 450 mm between the two tiers is what leaves room for legs when somebody on the upper bench is sitting rather than lying. The upper bench wants to be at least 600 mm deep so you can turn sideways on it, and the lower one 400 to 500 mm, which is enough to sit on and narrow enough to step over.
Does the ceiling height matter?
- It sets whether the upper bench is usable at all. In a 2,100 mm room the published layout leaves roughly 1,050 mm of clearance above the upper bench, which is enough to sit upright. Drop the ceiling and you lose that headroom one for one, because the bench height does not move. Harvia's own data sheet also gives a hard floor: 1,980 mm minimum room height for its electric heaters. This planner flags a room under that figure rather than sizing benches into a space a heater cannot legally go in.
Why does the seat count round down?
- Because two thirds of a seat is not a seat. A 1,828 mm bench divided by 600 mm is 3.048, and the honest answer is three people, not three and a bit. Rounding up would put four adults on a bench built for three and make every room in this planner look 25 percent larger than it is. The remainder is not wasted, it is the elbow room that makes 600 mm per person survivable.
Where do these dimensions come from?
- One published bench specification for the bench figures and one manufacturer data sheet for the room height, both linked below. Nothing in this planner is a rule of thumb somebody remembered. Where a figure is published as a range, such as the 400 to 500 mm lower bench depth, the planner shows the range rather than picking a number inside it.
Next
Once the size is settled
The room dimensions you land on here are the input to two other things: what heater the room needs, and what the whole build costs.