# Room Area Calculator

Floor, ceiling, walls, skirting and volume, all at once.

- Page: https://jianzhujisuan.com/en/room-area
- Category: Area and volume (https://jianzhujisuan.com/en/c/area-volume)
- Chinese version: https://jianzhujisuan.com/zh/room-area.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Room length 6 m, Room width 4 m, Clear height 2.8 m, Total opening area 4 m², Total door width 0.9 m): **Floor area 24.00 m²**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Room length | number | 6 | m |  |
| Room width | number | 4 | m |  |
| Clear height | number | 2.8 | m | Floor to ceiling, not storey height |
| Total opening area | number | 4 | m² | Door and window openings, added up |
| Total door width | number | 0.9 | m | Skirting stops at door openings |

## Formula

- **Floor / ceiling**: A = length × width
- **Perimeter**: P = 2 × (length + width)
- **Gross wall area**: A = P × clear height
- **Net wall area**: A = gross − openings
- **Skirting**: L = P − total door width
- **Volume**: V = length × width × clear height

## Worked example

A 6 × 4 m room at 2.8 m clear height with 4 m² of openings and a 0.9 m door: 24.00 m² floor and ceiling, 52.00 m² of net wall, 19.10 m of skirting, 67.20 m³ of volume and a wall-to-floor ratio of 2.17.

## Questions

### Why not just multiply floor area by 3 for walls?

The “times 3” rule is a fit-out shortcut that only holds for roughly square rooms at 2.7-2.8 m. The longer the room, the worse it gets: a 6 × 4 m room has a wall-to-floor ratio of 2.17 while 3 × 8 m gives 1.83 — nearly 20% apart. Wall area drives paint and filler quantities, and running short mid-job risks a colour mismatch.

### Should openings be deducted?

Yes for finishes such as paint, wallpaper and wall tiles. For filler and primer either is accepted and most estimators leave them in as margin. But the reveals — the inside faces of the opening — must be added: a 1.5 × 1.5 m window in a 200 mm wall has about 1.2 m² of reveal, so four windows is close to 5 m² that is easily forgotten.

### How do clear height and storey height differ?

Storey height runs between structural floors; clear height runs from finished floor to underside of ceiling, the difference being slab thickness plus floor build-up. A 3.0 m storey usually gives 2.7-2.8 m clear. Wall areas must use clear height — using storey height overstates by about 10%, two extra tubs of paint across ten rooms.

## Related tools

- [Wall Area and Paint Calculator](https://jianzhujisuan.com/en/wall-area): Net wall area with openings deducted, plus paint and filler.
- [Roof Area Calculator](https://jianzhujisuan.com/en/roof-area): True sloped roof area, rafter length and ridge rise from pitch.
- [Circle and Sector Calculator](https://jianzhujisuan.com/en/circle-calc): Circle area and circumference plus sector, arc, chord and segment.
- [Triangle Area Calculator](https://jianzhujisuan.com/en/triangle-area): Area from three sides, with angles, inradius and circumradius.
- [Battered Pit Volume Calculator](https://jianzhujisuan.com/en/pit-volume): Top dimensions and frustum volume from base size, depth and batter.
- [Cylinder Volume Calculator](https://jianzhujisuan.com/en/cylinder-volume): Volume, capacity, surface areas and weight for any cylinder.

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Generated by BuildCalc. All calculations run in your browser; no data is uploaded. Formulas follow national standards and common trade practice; local codes govern.