Quick answer
Wall area = 2 × (length + width) × height − openings. A 12 × 10 ft room with 8 ft ceilings and 40 ft² of windows and doors has 352 − 40 = 312 ft² of wall to paint, and a 120 ft² ceiling.
Enter the room length, width, ceiling height and the area of doors and windows. The calculator returns wall and ceiling areas.
Related tools: Room Area Calculator: Floor area of a rectangular room. Appliance Energy Cost Calculator: Electricity cost of running an appliance. Pool Fill Time Calculator: Hours to fill a pool at a flow rate.
How to use the Wall Area Calculator
- Enter room length (ft) (above 0).
- Enter room width (ft) (above 0).
- Enter ceiling height (ft) (above 0).
- Optionally, enter windows and doors (optional) (ft²) (0 or more).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Room length | A number, in ft | > 0 |
| Room width | A number, in ft | > 0 |
| Ceiling height | A number, in ft | > 0 |
| Windows and doors (optional) (optional) | A number, in ft² | ≥ 0 |
Formula and method
Formula
wall area = 2 × (length + width) × height − openings
IEEE-754 double precision; shown to the decimals indicated.
Ceiling area is also shown.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Room length = 12; Room width = 10; Ceiling height = 8; Windows and doors (optional) = 40.
| Result | Value |
|---|---|
| Wall area | 312 ft² |
| Ceiling area | 120 ft² |
Example 2
Inputs: Room length = 20; Room width = 15; Ceiling height = 9.
| Result | Value |
|---|---|
| Wall area | 630 ft² |
| Ceiling area | 300 ft² |
Example 3
Inputs: Room length = 8; Room width = 8; Ceiling height = 8; Windows and doors (optional) = 21.
| Result | Value |
|---|---|
| Wall area | 235 ft² |
| Ceiling area | 64 ft² |
The first line is the headline result (wall area). Below it the wall Area Calculator lists ceiling area, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Paint quantity
A gallon of paint typically covers about 350 ft² per coat, so 312 ft² needs about 0.9 gallons per coat, or 1.8 gallons for two. Buy slightly more for touch-ups and textured walls.
Openings
A standard door is about 20 ft² and a typical window 15 ft². Small openings can be ignored when estimating paint, as the saving is small.
How the result changes with room length
Holding every other input at the first worked example, this table changes only room length. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Room length | Wall area | Ceiling area |
|---|---|---|
| 6 | 216 ft² | 60 ft² |
| 12 | 312 ft² | 120 ft² |
| 24 | 504 ft² | 240 ft² |
| 48 | 888 ft² | 480 ft² |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Room length: entering "0" shows "Room length must be greater than 0." beside that field and no result.
- Windows and doors (optional): entering "999" shows "Openings cannot cover all of the walls." beside that field and no result.
Choosing between the Wall Area Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Room Area Calculator](/lifestyle/room-area-calculator/) | length and width | Room area |
| [Appliance Energy Cost Calculator](/lifestyle/appliance-energy-cost-calculator/) | power, hours used per day and electricity price | Cost per day |
| [Pool Fill Time Calculator](/lifestyle/pool-fill-time-calculator/) | pool volume and flow rate | Fill time |
| [Water Usage Calculator](/lifestyle/water-usage-calculator/) | people, water per person per day and days | Water used |
| [Lighting Lumens Calculator](/lifestyle/lighting-lumens-calculator/) | room area and target light level | Lumens needed |
Assumptions and limitations
- Openings cannot exceed wall area
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for room length and windows and doors (optional) to confirm this.
Frequently asked questions
How much paint do I need?
Divide the wall area by the coverage on the can.
Do I subtract baseboards?
No, baseboards are too small to matter for paint quantities.
Does it work in metres?
Yes, keep units consistent.
What does the Wall Area Calculator calculate?
Wall area of a rectangular room after openings. It returns Wall area and Ceiling area.
What formula does the Wall Area Calculator use?
wall area = 2 × (length + width) × height − openings. Ceiling area is also shown.
What do I need to enter in the wall Area Calculator?
You enter Room length (ft), Room width (ft) and Ceiling height (ft). Optional: Windows and doors (optional) (ft²).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Openings cannot exceed wall area.
What is an example of a wall Area result?
With room length 12, room width 10, ceiling height 8 and windows and doors (optional) 40, the wall area is 312 ft².
Related calculators
- Room Area Calculator — Floor area of a rectangular room.
- Appliance Energy Cost Calculator — Electricity cost of running an appliance.
- Pool Fill Time Calculator — Hours to fill a pool at a flow rate.
- Water Usage Calculator — Household water use from people and use per person.
- Lighting Lumens Calculator — Lumens needed for a room at a light level you choose.
- Water Bill Calculator — Water bill from usage, rate and a base charge you enter.
Sources
- ISO 8601-1: Date and time, representations for information interchange (calendar dates, ordinal dates and week dates)
- Gregorian calendar reform, papal bull Inter gravissimas (1582): the leap-year rule used for all dates
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.