Paint & Home Improvement calculator

Paint Calculator

Estimate wall paint, ceiling paint, primer, common litre pack sizes, and rough project cost from room dimensions or a custom wall area.

Category: HomeLast updated: 7 June 2026

Interactive calculator

Estimate paint, primer, packs, and cost

Start with room dimensions or an area you already measured. Then switch to cost mode to price the suggested litres without re-entering them.

What do you want to estimate? Use room dimensions, enter an area you already measured, or price the litres from either estimate.

Room dimensions

The wall formula uses the room perimeter and height. All door and window dimensions use the same feet or metres selection.

Room dimension unit Room length

Room width

Wall height

Doors and windows

Use average sizes when openings are similar. Enter zero for the count when none should be subtracted.

Number of doors

Average door width

Use the same feet or metres unit selected for the room. Average door height

Number of windows

Average window width

Use the same feet or metres unit selected for the room. Average window height

Ceiling

Include ceiling paint?

Ceiling paint coats

Coats, coverage, and surface

Default: 100 sq ft per litre per coat. Coverage on the paint can is more reliable, so edit the value and unit when you know them.

Wall paint coats

Two finish coats are a common planning choice, but follow the paint system instructions. Include one primer coat? Primer is often useful for new plaster, porous walls, repaired patches, or a strong colour change. Wall surface / colour condition This changes the planning buffer, not the stated coverage of a specific product. Coverage area unit Match the unit printed on the paint or primer container. Wall / ceiling paint coverage per litre

Default: 100 sq ft per litre per coat. Replace it with the container guidance when known.

Primer coverage per litre

Primer coverage is separate from finish-paint coverage.

Room dimensions estimate

9.39 L (2.48 US gal)

wall and ceiling paint after buffer

10% buffer

Gross wall area: 352 sq ft (32.7 sq m)
Openings subtracted: 45 sq ft (4.18 sq m)
Net paintable walls: 307 sq ft (28.52 sq m)
Wall paint before buffer: 6.14 L
Ceiling paint before buffer: 2.4 L
Primer after buffer: 4.7 L
Suggested buffer: 10%
Buy at least: 10 L
Pack / bucket idea: 1 pack: 1 × 10 L

What this means

For this room, the calculation uses 307 sq ft (28.52 sq m) of paintable wall area plus 120 sq ft (11.15 sq m) of ceiling. After 2 wall coats and a 10% planning buffer, allow about 9.39 L (2.48 US gal) of wall and ceiling paint.

Buying and budget guidance

Buy at least 10 L, or the next available pack size. A simple India-friendly pack idea is 1 × 10 L.

Next decision

Primer is estimated at one coat: about 4.7 L after buffer, so plan for at least 5 L. Then add the expected purchase to the Monthly Budget Calculator before hiring labour or buying materials.

Convert mixed measurements, check the paintable area, or plan the project budget.

Method used

Walls = 2 × (length + width) × height − doors/windows; litres = area × coats ÷ coverage; add ceiling separately, then apply the surface buffer.

What can change the real quantity

A 10% planning buffer allows for normal roller or brush loss and small touch-ups. The opening subtraction is reflected in the net paintable wall area. Coverage on the paint can is more reliable than the default because paint type, wall condition, application method, and colour change affect real use.

What to do next

Continue your decision

Formula, example, assumptions, and FAQs — open any section for the detail.

Formula

Room wall area and openings

Gross wall area = 2 × (length + width) × wall height · Net wall area = max(gross wall area − door area − window area, 0)

Measure wall area, not only floor area. Door area is count × average width × average height; window area uses the same method. If openings exceed the gross walls, the calculator clamps the result to zero and asks you to recheck the measurements.

Wall and ceiling paint

Paint litres = area × number of coats ÷ coverage per litre · Ceiling area = room length × room width

Wall and ceiling paint stay separate in the result because they can use different colours or products. The default 100 sq ft per litre per coat is only a planning estimate; coverage on the container is more reliable.

Primer and surface buffer

Primer litres = included surface area ÷ primer coverage · Buffered litres = calculated litres × (1 + buffer % ÷ 100)

Primer is estimated as one coat. The surface choice adds a transparent 10%, 20%, or 25% planning buffer; it does not claim to know the exact absorption or coverage of a wall or paint product.

Buying quantity and common litre packs

Buying quantity = paint litres after buffer rounded up to the next whole litre

The pack idea uses common Indian 1 L, 4 L, 10 L, and 20 L sizes. Actual pack availability varies, so compare the whole-litre estimate with available local packs and keep some matching paint for touch-ups.

Rough project cost

Total cost = paint litres × paint price/L + primer litres × primer price/L + labour + extra materials

Cost per sq ft and sq m divide that total by the entered painted area. Labour and preparation costs vary by city, wall condition, access, scope, and painter, so use an actual quote when possible.

Worked example

Example for a 12 ft × 10 ft room

A room is 12 ft long, 10 ft wide, and 8 ft high, with one 3 ft × 7 ft door and two 4 ft × 3 ft windows. The plan uses two wall coats, two ceiling coats, one primer coat, 100 sq ft/L coverage, and a normal-wall 10% buffer.

Calculation:Gross walls: 2 × (12 + 10) × 8 = 352 sq ft. Openings: 21 + 24 = 45 sq ft. Net walls: 307 sq ft. Ceiling: 120 sq ft. Paint before buffer: 307 × 2 ÷ 100 + 120 × 2 ÷ 100 = 8.54 L. Primer before buffer: 427 ÷ 100 = 4.27 L.

Result:After the 10% buffer, allow about 9.39 L of wall and ceiling paint and 4.70 L of primer. A practical buying check is at least 10 L of paint and 5 L of primer, adjusted to the packs actually sold and the coverage stated on those containers.

Assumptions

Room walls are treated as a rectangle with one length, width, and height.
Door and window dimensions use the same feet or metres unit selected for the room.
Custom wall area is treated as paintable area; when openings are not already excluded, subtract them separately for a tighter estimate.
Finish-paint coverage applies per coat and is entered by the user. The default is 100 sq ft per litre per coat.
Primer coverage is entered separately and primer is estimated as one coat across the included wall and ceiling surfaces.
The same finish-paint coverage is used for walls and ceiling in this simple estimator.
The surface condition changes only the suggested planning buffer: normal 10%, rough 20%, new plaster or porous 25%, and dark-to-light 20%.
Litres are the buying unit; US gallons are shown only as a global-friendly equivalent.
The cost mode uses prices and additions entered by the user and performs no currency conversion.

Common mistakes

Measuring only floor area instead of the full wall perimeter multiplied by height.
Mixing feet and metres across room, door, or window dimensions instead of using one unit system.
Forgetting to subtract doors and windows, or subtracting them twice when custom area is already paintable area.
Using one coat in the calculation when the project needs two or more coats.
Using a generic 100 sq ft/L default when the paint container gives a different coverage range.
Assuming rough walls, new plaster, repaired patches, or a strong colour change will use the same amount as a smooth previously painted wall.
Combining ceiling and wall paint without checking whether they use different products, colours, or pack sizes.
Buying exactly the decimal estimate with no allowance for roller loss, mixing, spills, or future touch-ups.
Comparing only price per bucket instead of price per litre and usable coverage.
Leaving labour preparation, putty, sanding, tape, sheets, rollers, brushes, or repair work out of the project budget.

Accuracy notes

Area conversion and arithmetic are deterministic, with area, litres, and money rounded to two decimals for display. The main uncertainty is real-world coverage: wall porosity, texture, preparation, paint type, application method, dilution, colour change, spills, and container-specific instructions can materially change usage. Pack suggestions are planning ideas, not purchase guarantees.

Frequently asked questions

How much area does 1 litre of paint cover?

This calculator starts at 100 sq ft per litre per coat, about 9.3 sq m, only as a planning estimate. Actual coverage depends on paint type, surface condition, colour change, dilution, and application method. Use the coverage printed on the container when available.

Should I subtract doors and windows?

Yes, when you know their approximate size. In room mode, enter the count and average dimensions. In custom-area mode, say whether openings are already excluded so the result can warn you when the area may still be too high.

Does the calculator include the ceiling?

Only when you select it in room mode. Ceiling area is length × width, and ceiling litres are shown separately from wall paint before both are combined for the buying total.

When should I include primer?

Check primer for new plaster, porous or repaired walls, bare surfaces, stains, and major dark-to-light colour changes. Follow the selected paint system and surface-preparation instructions rather than assuming primer is always optional or always required.

Why does rough or new plaster add a buffer?

Texture and porosity can increase material use and application loss. The buffer is a cautious planning allowance, not a claim of exact coverage. A test patch and the product guidance are more reliable.

How are 1 L, 4 L, 10 L, and 20 L packs suggested?

The buffered paint quantity is rounded up to a whole litre and shown as a simple combination of common Indian pack sizes. Availability differs by product and market, and a larger pack may be simpler when you want matching paint for touch-ups.

Can I use this paint calculator outside India?

Yes. Use feet or metres, square feet or square metres, edit coverage in the unit printed on the container, and change the currency symbol. Litres remain the main quantity, with a US-gallon equivalent for reference.

Does the cost estimate include labour?

Only when you enter a labour amount. Rates vary by city, access, wall repair, preparation, number of coats, and painter. The calculator has no labour-rate database and does not provide a quotation.

This calculator provides a rough material and cost estimate only. It does not inspect the surface, select a paint system, verify curing or moisture conditions, replace container instructions, recommend a brand, or provide a contractor quote. Confirm important quantities with product guidance and an experienced painter or supplier.Read the full disclaimer.

Last updated: 7 June 2026More Home calculators