Paint Calculator
Calculate how many litres of paint you need for walls and ceilings. Add multiple rooms, subtract doors and windows, select the number of coats, enter paint coverage and estimate the total paint cost.
Paint Project Details
Add each room and enter its length, width and wall height.
Paint Calculation Summary
Room-by-Room Paint Area
See the estimated wall and ceiling area for each room.
| Room | Length | Width | Wall Height | Wall Area | Ceiling Area |
|---|
How to Use the Paint Calculator
Enter the length, width and wall height of each room you want to paint. You can add multiple rooms and the calculator combines the total wall area.
Then enter the number of doors and windows so their area can be deducted. Choose the number of paint coats, enter the coverage stated by the paint manufacturer and select whether ceilings and primer should be included.
How Is Paint Quantity Calculated?
For a rectangular room, the approximate wall area is calculated using the perimeter of the room multiplied by the wall height.
Door and window areas are then deducted.
The paint requirement is then estimated using:
Paint Calculator Example
Suppose a room measures:
- 5 metres long;
- 4 metres wide;
- 2.4 metres high.
The wall area is:
2 × (5 + 4) × 2.4 = 43.2 m²
If doors and windows total 5 m²:
43.2 − 5 = 38.2 m²
For two coats:
38.2 × 2 = 76.4 m² of coverage required
If the paint covers 14 m² per litre:
76.4 ÷ 14 ≈ 5.46 litres
A practical purchase quantity would normally be rounded up to suit available paint tin sizes.
How Much Area Does 1 Litre of Paint Cover?
Paint coverage varies by product, surface type and application method. Many paints provide an estimated coverage figure in square metres per litre.
Always use the manufacturer’s stated coverage rate for the paint you are buying.
How Many Coats of Paint Do I Need?
Two coats are common for many interior painting projects, but the actual requirement can depend on:
- Existing wall colour;
- New paint colour;
- Surface condition;
- Paint quality;
- Primer use; and
- Manufacturer recommendations.
Should I Subtract Doors and Windows?
If those areas will not be painted with the wall paint, subtracting them can improve the estimate.
For small projects, some people leave them included because the extra paint can provide a useful allowance for touch-ups and wastage.
How to Calculate Ceiling Paint
For a rectangular ceiling:
The calculator adds each room’s ceiling area when the ceiling option is enabled.
Do I Need Primer?
Primer may be useful when painting new plaster, repaired surfaces, stained walls, porous materials or when making major colour changes.
This calculator can estimate one coat of primer using the same coverage rate entered for paint. For purchasing, use the actual coverage figure of your chosen primer product.
Why Add Extra Paint Allowance?
An additional allowance can help account for:
- Roller and brush losses;
- Surface absorption;
- Touch-ups;
- Uneven application;
- Spillage; and
- Future repairs.
A 5% to 10% allowance is a useful planning estimate for many projects.
Can I Use This Calculator for Multiple Rooms?
Yes. Click Add Another Room and enter the dimensions of each room separately.
The calculator combines all wall and ceiling areas automatically.
Can I Use This Calculator for Interior Painting?
Yes. It is designed primarily for interior rooms, walls and ceilings.
Can I Use It for Exterior Walls?
You can use the same basic area method for rectangular exterior walls, but exterior buildings often have more irregular surfaces, gables, doors, windows and different paint coverage requirements.
Does the Calculator Include Labour Cost?
No. The estimated cost is based only on the paint price per litre entered.
Other costs may include:
- Professional painting labour;
- Primer;
- Brushes and rollers;
- Drop sheets;
- Masking tape;
- Paint trays;
- Wall preparation;
- Filler and sanding materials; and
- Ladders or access equipment.
Paint Calculator Assumptions
This calculator assumes:
- Rooms are rectangular;
- Wall height is uniform;
- Door and window areas are estimated using an average size;
- The entered coverage rate applies evenly;
- Coverage is entered in square metres per litre;
- Ceiling area is length × width;
- Primer is estimated as one coat;
- The same paint coverage rate is used for primer when selected;
- No labour cost is included; and
- Results are planning estimates only.
Related Property & Construction Calculators
Paint Calculator FAQs
How do I calculate how much paint I need?
Calculate the wall area, subtract doors and windows, multiply by the number of coats and divide by the paint coverage in square metres per litre.
How much paint do I need for two coats?
Multiply the paintable surface area by two before dividing by the paint’s stated coverage rate.
Can I add multiple rooms?
Yes. Add each room separately and the calculator combines all room areas automatically.
Does the calculator subtract doors and windows?
Yes. Enter the number of doors and windows and their average area to subtract them from the wall area.
Can I include ceilings?
Yes. Select the ceiling option and the calculator adds the floor-plan area of each room as ceiling area.
Can this calculator estimate paint cost?
Yes. Enter a price per litre to estimate the total material cost.