The depth a row needs is three numbers, not one
Seating catalogues publish a depth. It is the depth of the object sitting upright in a showroom, and it is the number everyone draws the riser to. The depth a row actually occupies is that figure plus whatever the mechanism travels when someone reclines, plus the clear floor somebody needs to walk behind a reclined seat and reach their own place in the dark.
A 38 inch seat with 14 inches of recline travel and a 20 inch walkway takes 72 inches of room length — six feet per row, not three and a bit. Two rows plus nine feet of clearance in front of the first is 21 feet of room, which is more than a lot of rooms have. That arithmetic is why theatre rooms end up with two rows rather than three, and why finding out about it after the platform is built is expensive.
The recline figure varies enormously by mechanism. A wall-hugger design slides forward as it reclines and needs only a few inches behind it; a traditional mechanism tips backward and needs considerably more. It is the single biggest lever on the layout and it is a specification you can read before buying, so read it before drawing the tier.
Why the second row needs more riser than people build
This is the part worth understanding before anything gets framed, and it is genuinely counter-intuitive. The sightline from the back row does not have to clear the seat in front. It has to clear the head of the person in it, and that head is roughly four to five inches above their eyes, sitting on a body whose eyes are already forty-odd inches off the tier they are on.
So the rise needed is not the difference in seat height. It is enough that the eye of the person behind sits above a line drawn from their eye, over the top of the head in front, down to the bottom of the screen — and because that line is nearly flat when the rows are close together and the screen is far away, a small clearance at the head in front costs a lot of height at the back. Rooms built with a six inch riser routinely find that row two is watching the bottom third of the picture through somebody hair.
Working out the number properly is a geometry problem with the screen bottom edge, the row spacing and the seated eye height in it, and the audience sightline and riser calculator solves it directly. Do that first. This page takes the height as an input on purpose, because a riser height chosen for tidiness is the most common reason a second row does not work.
The surfaces a plan view cannot show
Draw a riser on a floor plan and you see a rectangle. Order carpet for that rectangle and you will be short, because the platform has a front face, two exposed sides that get taller toward the back of the room, and an edge that the finish has to wrap over.
| Surface | How it is worked out | Often forgotten |
|---|---|---|
| Deck top | Room width times tier depth, per tier | No |
| Front face | Room width times the tier height | Sometimes |
| Exposed sides | Two per tier, tier depth times height above the floor | Nearly always |
| Nosing wrap | Overhang at the edge, times the width | Nearly always |
On a two tier room the vertical faces are commonly a quarter to a third of the total finish area. They are also the surfaces at eye level for anyone standing up, so they are the ones a visitor actually looks at, and the ones where a seam or a shortage shows.
The hollow box problem
A riser is a sealed volume of air under a thin sheet of decking, in a room whose entire purpose is to put large amounts of low frequency energy into the air. A 15 by 6 foot tier a foot high is 90 cubic feet; two of them, with the back one two feet up, is 270. That is a drum with the audience sitting on it.
What people do about it is decided before the deck goes down, because afterwards the options are all destructive. Bracing the cavity into smaller compartments raises the frequency at which the deck panel wants to resonate and reduces how much it moves. Filling the cavity damps it. Doing both is common. Some rooms deliberately leave a tier partly hollow and use it, which is a defensible choice made on purpose rather than by default.
The same cavity is also the only sensible route for cable to reach the back row, and for the power that a row of motorised seats needs. Plan the chase and an access panel while it is still an open box. Working out how much cable that route actually consumes is the AV cable run calculator, and it is always more than the straight line across the room.
What this page will not tell you
It will not size a single piece of framing. How the platform is built, what depth and spacing the members need, and whether the whole thing carries a row of loaded recliners plus the people in them are structural questions answered by the adopted code, the span tables it references, and where necessary an engineer. Once someone has decided what the members are, the floor joist calculator counts them.
It also says nothing about what the step, the edges and the aisles are required to be. Step rise and run, edge marking, guards, handrails, aisle width, aisle lighting and egress are set by the adopted code and the authority having jurisdiction where you live, they differ between jurisdictions, and they are not a matter of preference. Ask the building department before framing, because a riser is a step in a dark room that people walk on carrying things, and the edges at the sides and the back have nothing to stop a fall.
For the rest of the room, the seating distance that sets the front row position is the viewing distance calculator, and where the speakers land relative to the seats is the speaker placement calculator.
Questions people ask
How deep does a home theater riser need to be?
Deep enough for the seat at its reclined depth plus the walkway behind it, which for common recliners lands somewhere around six feet per row rather than the three or four the catalogue depth suggests. The three components are the upright seat depth from the specification, the extra travel the mechanism needs when reclined, and clear floor for someone to walk behind a reclined seat to reach their place. Wall-hugger mechanisms cut the third component substantially because they slide forward instead of tipping back. Get all three from the seating specification before drawing the platform, because the recline figure is the one that changes the answer most and it is the one nobody looks up.
How high should the second row riser be?
Higher than most people build, and the reason is that the sightline has to clear the head in front rather than the seat in front. Seated eye height on the tier, plus four or five inches to the top of the head, is what the row behind has to see over, and because the rows are close together relative to the distance to the screen that line is nearly flat — so a modest clearance at the head in front costs a surprising amount of height at the back. A six inch riser very often is not enough. Work the actual geometry with the audience sightline and riser calculator, using your screen bottom edge and your row spacing, and take the height from that rather than from a round number.
How many rows will my room take?
Take the room length, subtract the distance from the screen wall to the front row, and divide what is left by the depth each row needs. With a 20 foot room, 9 feet to the front row and 72 inches per row, that leaves 11 feet and gives one row plus a bit — so two rows total only if something gives. The levers are the front clearance, the walkway width and a seat with less reclined travel. Shrinking the walkway is the tempting one and the one that gets regretted, because that is the space people move through with the lights off. Remember also to measure the length after wall treatment is on, since a treated front and back wall can take several inches out of the number you started with.
Should the riser be hollow or filled?
That is a decision to make before the deck goes down, because afterwards every option is destructive. A hollow riser is a large sealed volume of air under a thin panel, in a room designed to put low frequency energy into the air, and it will move and resonate. Bracing the cavity into smaller compartments and filling it are the two common responses and they are frequently done together. Some rooms leave part of the cavity as usable space on purpose, which is fine as long as it is a decision rather than an oversight. Either way, run the cable chase and fit an access panel while it is still an open box.
Do I need a step up onto the riser, and what size?
This page will not answer the second half of that and neither should any web page. Step rise and run, whether an intermediate step is required, edge marking, guards, handrails and lighting for a raised seating platform are set by the adopted code and the authority having jurisdiction where you are, and they vary between jurisdictions. The arithmetic the calculator will do is divide your tier height by a step rise you specify, which tells you how many steps that height makes and nothing about whether it is permitted. Ask the building department before framing. The plain hazard is worth naming even so: a riser is a step in a room where the lights are deliberately off, and the sides and the back have nothing to stop a fall.