Measure a room properly
Length, width and floor-to-ceiling height. Openings are deducted at standard sizes.
How this calculator works
- Floor and ceiling = length × width, in square feet, converted to square metres by dividing by 10.7639.
- Perimeter = 2 × (length + width).
- Gross wall = perimeter × floor-to-ceiling height. Use the real slab-to-slab-minus-ceiling height, not the nominal one.
- Openings. One standard flush door is 3 ft × 7 ft = 21 sq ft. One standard window is 5 ft × 3 ft = 15 sq ft. Both are deducted from gross wall area.
- Skirting = perimeter − (doors × 3 ft), because skirting stops at each door opening.
- Tiles = ceiling(floor area × 1.08 ÷ 3.875). A 600 × 600 mm tile is 1.9685 ft square, so 3.875 sq ft.
- Paint = (net wall + ceiling) × 2 coats ÷ 110 sq ft per litre. That coverage is the realistic figure for emulsion on puttied plaster, not the tin's optimistic one.
| Element | Standard size used | Note |
|---|---|---|
| Flush door | 3 ft × 7 ft = 21 sq ft | Main doors are often 3.5 ft wide — add 3.5 sq ft each |
| Window | 5 ft × 3 ft = 15 sq ft | Mumbai bedroom windows vary from 12 to 24 sq ft |
| Skirting deduction | 3 ft per door | Sliding and wardrobe openings deduct more |
| 600 × 600 mm tile | 3.875 sq ft | Nominal; grout joints are ignored |
| Emulsion coverage | 110 sq ft per litre per coat | On putty; bare plaster drinks 20% more |
Design and build under one accountable roof
Worked example — the default room
A 14 ft × 11 ft bedroom with a 10 ft ceiling, one door and two windows — a common Mumbai 2BHK master.
| Quantity | Arithmetic | Result |
|---|---|---|
| Floor area | 14 × 11 | 154 sq ft (14.3 sq m) |
| Perimeter | 2 × (14 + 11) | 50 ft |
| Gross wall area | 50 × 10 | 500 sq ft |
| Openings | (1 × 21) + (2 × 15) | 51 sq ft |
| Net wall area | 500 − 51 | 449 sq ft |
| Skirting run | 50 − (1 × 3) | 47 ft |
| Floor tiles | ceiling(154 × 1.08 ÷ 3.875) | 43 tiles |
| Emulsion, two coats | (449 + 154) × 2 ÷ 110 | 11 litres |
How to measure a room so the numbers are right
- Measure at floor level, twice
Take the length and width at skirting height, then again at waist height. Mumbai walls in older buildings are frequently out of square by 50–75 mm across a room, and the smaller of the two readings is the one your furniture has to fit.
- Measure the real ceiling height
Floor to underside of slab, then subtract any existing false ceiling. A 10 ft nominal slab in a 1990s Mumbai building often gives 9 ft 6 in clear after the beam drop, and beams are usually the lowest point.
- Count openings honestly
Include the wardrobe opening, the AC sleeve, the electrical panel and the safe niche. Each is area that will not be painted, tiled or panelled.
- Note anything that is not a rectangle
Bay windows, ducts, columns and niches. Break the room into rectangles, run each through the calculator and add the results — that is exactly what an estimator does.
What each number is actually used for
Floor area drives flooring, the rug size and the air conditioning tonnage. Ceiling area drives the false ceiling and the ceiling paint, and it is the same figure as the floor only if the ceiling is flat — a peripheral cove adds about 8% of surface, a full stepped ceiling considerably more. Perimeter drives skirting, cornice, cove lighting and the length of any wall panelling run.
Net wall area is the one contractors quote against and the one most often disputed, because some quote gross and deduct nothing. On a 14 × 11 ft bedroom the difference between 500 and 449 sq ft is 51 sq ft — about ₹3,000 of painting. Multiply that across seven rooms and it is a real number. Ask whether the rate is on gross or net wall area before you compare two quotes.
Skirting run is the sleeper. It is measured in running feet, quoted at ₹120–450 per foot depending on material, and it appears on every wall of every room, so a 2BHK easily carries 180 running feet of it. At ₹280 per foot that is ₹50,000 — enough to be worth checking whether the quantity in your BOQ matches the actual perimeter of your flat.
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
- Non-rectangular rooms — split them into rectangles and add the results.
- Sloped, stepped or double-height ceilings, where the wall area is higher than perimeter × height.
- Columns, ducts and beam drops, which reduce floor area and increase the surfaces to finish.
- Skirting behind wardrobes and beds, which most contractors will omit unless you ask for it.
- Tile wastage above 8% — a room with many corners, a diagonal layout or a large-format tile will need 10–15%.
- For paint specifically, the paint quantity calculator accounts for primer, putty and finish type.
Selected work by Greenbox Design Studio. Tap any image to enlarge.
Frequently asked questions
How do I calculate the area of a room in square feet?+
Multiply length by width, both in feet. A 14 ft by 11 ft room is 154 sq ft. If the room is not a rectangle, split it into rectangles, work each out and add them together.
How do I calculate wall area for painting?+
Perimeter × ceiling height, then deduct 21 sq ft per door and 15 sq ft per window. For a 14 × 11 ft room at 10 ft with one door and two windows that is 500 − 51 = 449 sq ft of paintable wall, plus 154 sq ft of ceiling if you are painting that too.
Why is my room's area different from the builder's figure?+
Because the builder's figure is usually built-up or super built-up area, which includes wall thickness and a share of common space. A measured room area is carpet area, and it will be 25–40% lower than the brochure number for the flat as a whole.
How many tiles do I need for a room?+
Floor area ÷ tile area, plus 8–10% for cuts and breakage. A 600 × 600 mm tile covers 3.875 sq ft, so a 154 sq ft room needs 43 tiles including wastage. Buy from one batch and keep four spares for future repairs.
What ceiling height should I use if there are beams?+
Use the clear height under the lowest beam for anything that runs across the room — a false ceiling, a wardrobe loft, a curtain track. Use the full slab height only for the wall panels between the beams.