Plan your home theatre
Room dimensions first. Everything else is derived from them.
How this calculator works
- Usable depth = room length − 2 ft rear clearance − 1.5 ft screen wall allowance (the screen wall carries the left, centre and right speakers and, in an acoustically transparent setup, the screen sits in front of them).
- Seating block = rows × 4 ft. Four feet per row covers a recliner in the reclined position plus circulation.
- Front-row distance = usable depth − seating block.
- Image width = front-row distance ÷ viewing standard, then capped at room width − 4 ft so the screen never runs into the side walls.
- Diagonal = width × 12 ÷ 0.87157, snapped to the nearest standard screen size from 92 to 165 inches.
- Throw distance = image width × 1.4, the mid-point for a standard long-throw projector lens. Check it against your projector's own throw ratio.
- Left and right speakers are placed at ±26° from the centre seat, which is the middle of the 22–30° ITU band.
| Element | Allowance used | Why |
|---|---|---|
| Rear wall clearance | 2 ft | Rear surrounds and a walkway behind the last row |
| Screen wall depth | 1.5 ft | LCR speakers, screen frame, cable run |
| Depth per seating row | 4 ft | Recliner in reclined position plus circulation |
| Width per seat | 2 ft | Standard theatre recliner is 22–26 in wide |
| Side clearance to screen | 2 ft each side | Keeps the image off the side-wall reflections |
| Riser per rear row | 12 in | Clears the head of the row in front |
| Acoustic treatment | 25% walls + 40% ceiling | First reflection points and the front half of the ceiling |
Design and build under one accountable roof
Worked example — the default room
| Step | Arithmetic | Result |
|---|---|---|
| Usable depth | 20 − 2 − 1.5 | 16.5 ft |
| Seating block | 2 rows × 4 ft | 8 ft |
| Screen to front row | 16.5 − 8 | 8.5 ft |
| Image width at THX 1.2 | 8.5 ÷ 1.2 | 7.08 ft |
| Width cap from room | 13 − 4 | 9 ft — not binding |
| Diagonal | 7.08 × 12 ÷ 0.87157 | 97.5 in |
| Nearest standard screen | from 92, 100, 106 | 100 in |
| Seats | floor((13 − 2) ÷ 2) × 2 rows | 10 seats |
| Throw distance | 7.26 ft × 1.4 | 10.2 ft |
What separates a home theatre from a TV room
Three things, and only one of them is the screen. The first is light control: a theatre has no uncontrolled daylight, which in a Mumbai flat means a blackout roller behind a pelmet, not a curtain. The second is acoustics. A rectangular room with hard walls and a tiled floor has a reverberation time around 0.8 seconds, roughly twice what you want, and no amount of speaker budget fixes it. Absorption at the first reflection points on both side walls, on the front half of the ceiling, and a bass trap in each front corner will do more for the sound than doubling the amplifier.
The third is the seating geometry this calculator is about. The single most common mistake we see in Mumbai home theatres is a screen chosen first, to fill the wall, with the seating then placed wherever it fits. The result is a front row at 6 ft from a 133-inch image, which is a 60-degree field of view — unwatchable for anything longer than a trailer.
A practical note on Indian flats: a true dedicated theatre needs a room you can seal, and that room then needs its own air conditioning, because ten people and a projector in a sealed 250 sq ft box is a heat load. Size the indoor unit about 20% above what the floor area alone suggests, put it at the rear of the room, and specify a low-noise unit. Fan noise is the complaint we hear most often about finished theatres.
Every constant on this page comes from Greenbox site records — measured drawings, signed BOQs and completion certificates from projects delivered between 2023 and 2026 — rounded to the figures an estimator would actually write down. We publish them so the arithmetic can be audited rather than trusted. Treat the output as a planning figure: accurate enough to brief a landlord, a bank or a family, and not accurate enough to sign a contract against.
What this tool does not cover
- Equipment cost — projector, screen, amplifier, speakers, seating and automation, which together typically exceed the construction cost.
- Structural and civil work, including any change to the room's walls or the slab for a riser.
- Electrical load. A projector, amplifier and subwoofer need dedicated circuits and clean earthing.
- Detailed acoustic modelling. The 25% and 40% allowances here are a starting budget, not a treatment design.
- Ceiling height under 8.5 ft with a riser, where the rear row may not clear comfortably — check the headroom figure the tool reports.
- For a TV rather than a projector, use the TV size calculator.
Selected work by Greenbox Design Studio. Tap any image to enlarge.
Frequently asked questions
What size room do I need for a home theatre?+
A minimum of about 16 ft long by 11 ft wide for a single row with a 92-inch screen. Twenty by thirteen feet comfortably takes two rows and a 100-inch image. Below 16 ft of length you are building a TV room, which is a perfectly good thing to build — just not the same thing.
How far should the front row be from the screen?+
1.2 times the image width for THX reference, 1.5 times for SMPTE. For a 7 ft wide image that is 8.4 ft or 10.5 ft. Closer than 1.2× and the eye has to travel across the frame; further than 2× and the immersion is gone.
How high should a home theatre riser be?+
Twelve inches per row. That clears the head of the person in front for a normally proportioned seated adult. Check the headroom over the rear row before committing — a 12-inch riser in a 9 ft room leaves 8 ft, which is fine, but two risers in the same room does not.
Do I need acoustic treatment in a home theatre?+
Yes, and it matters more than the speakers. A hard-surfaced room has roughly twice the reverberation time you want. Treat the first reflection points on both side walls, the front half of the ceiling and the two front corners, and the same equipment will sound like a different system.
Can a home theatre work in a Mumbai flat?+
Yes, in a spare bedroom, a converted third bedroom or a basement in a villa. The two constraints are light control, which a blackout roller behind a pelmet solves, and neighbours — a subwoofer in a shared-wall building needs isolation pads and a sensible level discipline after 10 pm.