A sauna bench should be 20 to 24 inches deep. Twenty inches is the minimum for sitting comfortably with your back against the wall. Twenty-four inches is what you need to actually lie down without your shoulders hanging off the front edge. For the upper bench in any sauna you plan to lie down in, build it 24 inches deep.

That's the short answer. The reason it matters — and the reason it's worth checking carefully — is that most sauna kits ship benches that are 18 to 20 inches deep, and a lot of people don't notice until they're already inside trying to get comfortable.

What "Bench Depth" Actually Means

Bench depth is the front-to-back measurement of the bench — how far the seating surface extends from the wall out toward the middle of the room. It's the dimension that decides whether you can lie down, lean back, or just perch on the edge.

People sometimes call this "bench width," which is confusing because width can also mean how long the bench is along the wall (how many people fit side by side). To keep it clear: in this post, depth is front-to-back, and that's the number that controls comfort. When a sauna kit lists a bench as "20 inches," that's almost always the depth.

The Numbers: Sitting vs. Lying Down

Here's how depth translates to what you can actually do on the bench:

The jump that matters is from 20 to 24 inches. Sitting works fine at 20. But the moment you lie down, those extra four inches are the difference between your whole upper body being supported and your shoulders dangling over the edge.

Why 24 Inches — The Shoulder Problem

When you sit, your back is against the wall and your weight runs straight down through your hips. You don't need much depth. But when you lie down on your back, the widest part of your body — your shoulders — has to fit on the bench, and your arms need somewhere to rest too.

Adult shoulder width runs roughly 16 to 19 inches across for most people, and that's just the bony part. Once you're lying flat, your shoulders splay outward and your arms fall to your sides, so the footprint your upper body actually needs is wider than the standing measurement. On a 20-inch bench, your back fits but your shoulders and arms end up right at the front edge or hanging off it. You feel like you're balancing instead of relaxing, and you end up curling up or hugging your arms in to stay on.

At 24 inches, your shoulders sit fully on the wood with a couple inches to spare, and your arms have somewhere to go. That's the whole point of lying down in a sauna — letting go completely — and you can't do it on a bench that makes you hold a position.

This is also why a deep bench matters more the more you use the sauna. A quick 10-minute sit, you'll tolerate a shallow bench. But if you like long sessions, stretching, or sharing the sauna with a partner where both of you want to lie down, 24 inches stops being a nice-to-have.

Why Most Sauna Kits Are Too Shallow

This is the part worth slowing down on, because it's where people get caught.

Kit manufacturers have two reasons to build shallow benches: cost and footprint. A shallower bench uses less wood, which trims the material cost on every unit they ship. And a shallower bench lets them fit benches into a smaller cabin while still calling it a "2-person" or "4-person" sauna. A barrel sauna or a compact prefab cabin can claim more seats if each bench only has to be 18 inches deep.

The result is that a lot of kits — especially barrel saunas and budget prefab cabins — come with benches in the 16 to 20 inch range. They're fine to sit on. They are not deep enough to lie down on. And the product photos almost never show someone lying flat, because it wouldn't look comfortable.

A few things to check before you buy any kit:

• Find the actual bench depth in the specs. Not the cabin size — the bench depth, front to back. If it's not listed, ask. If they won't give you a number, that tells you something.
• Look for 24 inches on the upper bench if lying down matters to you. If the upper bench is 20 or less, you're buying a sit-only sauna.
• Be skeptical of seat counts. A "4-person" sauna with 18-inch benches seats four people sitting upright, shoulder to shoulder. It does not fit two people lying down.
• Barrel saunas are the worst offenders. The curved wall eats into bench depth, and the geometry makes a deep flat bench hard to build. If lying down is a priority, a barrel is usually the wrong shape.

Lower Bench Depth Is Different

Everything above is about the upper bench — the one you sit and lie on. The lower bench has a different job, so it gets a different depth.

The lower bench mostly works as a step up to the top bench, a footrest when you're sitting up top, and an occasional cooler seat. For that, 14 to 18 inches is plenty. Go to 18 inches if people will actually sit on it for full sessions; stick to 14-16 if it's mainly a step. Building the lower bench as deep as the upper one just wastes wood and eats floor space you'd rather keep open.

How Depth Gets Built

A sauna bench is usually built from 2×4 lumber laid flat, so each board gives you a 3.5-inch-wide surface. To hit a 24-inch depth, you're looking at roughly six 2×4s laid side by side, plus small gaps between boards and a slight front overhang. Six boards is about 21 inches of wood, and the gaps and overhang carry you the rest of the way to 24.

Those gaps matter for more than depth: leave about 1/4 to 3/8 inch between boards so air can move under the bench and water drains instead of pooling. And let the front board overhang the support frame by an inch or two — it gives you a rounded edge to grip climbing up and keeps the bare frame off your skin.

If you're building benches yourself rather than buying a kit, depth is essentially free to get right — it's a matter of adding one more board to the frame. The cost difference between a 20-inch and a 24-inch bench is one 2×4 per run. That's the whole reason it's frustrating to see kits skimp on it.

Quick Reference

Frequently Asked Questions

How deep should a sauna bench be?

An upper bench should be 20 to 24 inches deep. Use 24 inches if you want to lie down comfortably — that's the depth that supports your shoulders so they don't hang off the front edge. A lower bench or step can be 14 to 18 inches.

How deep does a sauna bench need to be to lie down?

24 inches. At 20 inches or less, your back fits but your shoulders and arms end up at or over the front edge, so you can't fully relax. The extra four inches between a 20-inch and a 24-inch bench is exactly what supports your upper body when you're flat.

Why are sauna kit benches so shallow?

Cost and footprint. A shallower bench uses less wood and lets the manufacturer fit more "seats" into a smaller cabin. Many kits — especially barrel saunas and budget prefab cabins — ship 16 to 20 inch benches that are fine for sitting but too shallow to lie down on. Always check the listed bench depth before buying.

Is bench depth the same as bench width?

Not quite. Depth is the front-to-back measurement (how far the bench sticks out from the wall), which controls whether you can sit back or lie down. Width usually refers to how long the bench runs along the wall, which controls how many people fit side by side. When a kit lists a single bench dimension, it's almost always the depth.

How deep should the lower bench be?

14 to 18 inches. The lower bench mainly serves as a step, a footrest, and a cooler seat, so it doesn't need the full depth of the upper bench. Use 18 inches if it'll get real seating use, 14-16 if it's mostly a step.

Depth is only one piece of getting benches right — height matters just as much, and for a different reason. For upper and lower bench heights at every ceiling height, plus layout and material choices, see the full guide on sauna bench height and dimensions.

If you'd rather not work out the dimensions yourself, the Sizing module covers bench layouts for common room sizes, or get a design package with complete bench specs drawn up for your exact space.