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Renovation & Construction

Paint Calculator

Estimate how much paint you need for a room based on its dimensions, doors, windows, and number of coats.

  • Answers as you type
  • Every formula cited
  • Calculated in your browser
SettingsSettings for this calculationUS
Market
Imperial · sales tax
Pick how the walls are given: as a room, as a length and height, or as a ready area.

The litres follow the wall surface whichever way it arrives. A feature wall, a hallway or a room with a bay suits the length and height; a stairwell or a gable end suits an area worked out beforehand.

The length of the room, wall to wall.

Measure along the floor from one wall to the opposite wall. If the room isn't a perfect rectangle, measure the longest straight run and treat alcoves separately.

Tools needed: Tape measure or laser measure

The width of the room, wall to wall.

Measure along the floor perpendicular to the length, from one wall to the opposite wall.

Tools needed: Tape measure or laser measure

Floor-to-ceiling height.

Measure from the floor to the ceiling at one wall. Standard residential ceilings are commonly 2.4 m (8 ft); measure yours if it might differ.

Tools needed: Tape measure or laser measure

Doors are not painted with wall paint, so their area is subtracted.

Count only doors on the walls you're painting. Each one takes off the area of one door, set further down.

Windows are not painted with wall paint, so their area is subtracted.

Count the windows in the walls you're painting. Each one takes off the area of one window, set further down.

What each door takes off the walls. The default suits a standard interior door with its frame.

The default is the allowance paint estimators use for a standard interior door and its frame. A double door, a wide opening or a door to a garden takes off more: measure its width and height and enter width times height. With doors of different sizes, enter their average — the total taken off is then exact.

What each window takes off the walls. The default suits a typical window.

The default is a typical window's allowance. A picture window or a sliding patio door takes off far more, and a small landing window less: measure the opening and enter its width times its height. With windows of different sizes, enter their average — the total taken off is then exact.

Most walls need 2 coats for even, opaque coverage.

One coat is rarely enough for full coverage, especially over a different existing color. Dark-to-light color changes or unprimed drywall may need a 3rd coat.

The area one unit of your specific paint covers — the spread rate printed on the tin.

This varies by brand, finish and the surface being painted. North American wall paints are commonly rated at about 350 to 400 sq ft per gallon (8.6 to 9.8 m² per litre), while UK and European emulsions often state up to 13 to 17 m² per litre. The default, 10 m² per litre (about 400 sq ft per gallon), is a middle figure; the tin's own stated coverage is the one to use.

Estimated paint needed

1.704 gal

High confidence
Gross wall area
392 sq ft
Doors + windows area (subtracted)
51.13 sq ft
Paintable area
340.87 sq ft
Total area to coat
681.74 sq ft
Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

  • Standard interior door/window opening allowances used by professional estimators (~21 sq ft door, ~15 sq ft window)
  • Paint coverage rate varies by product — always check your specific paint can's label for its stated coverage per liter/gallon

Inputs used

Surface to Paint
A room's four walls (length, width, height)
Length of Wall to Paint
49 ft
Height Painted
8 ft
Wall Area to Paint
390 sq ft
Room Length
13 ft
Room Width
11.5 ft
Wall Height
8 ft
Number of Doors
1
Number of Windows
2
Area of One Door
20.99 sq ft
Area of One Window
15.07 sq ft
Number of Coats
2
Paint Coverage
400 ft²/gal

Intermediate steps

Gross wall area
392 sq ft
Doors + windows area (subtracted)
51.13 sq ft
Paintable area
340.87 sq ft
Total area to coat
681.74 sq ft
Final result1.7 gal

What this calculation does not cover

  • One area stands for every door and one for every window, so a room with a sliding patio door and a small landing window takes the same off the wall for each; enter the average of the openings a field stands for and the total taken off is exact, though no single wall's share is.
  • Measured as a room, the gross wall area is 2 × (length + width) × height, a closed rectangle with one height on all four walls; an L-shaped room, a chimney breast, a bay recess or a stairwell wall goes in as a run of wall and its height, or as an area you have measured.
  • Skirting boards, architraves and picture rails stay inside the paintable area even though they are usually finished in trim paint, and no separate volume is worked out for the door leaves and window frames whose area was taken away.
  • A single spread rate multiplies every coat alike, so the thirstier first pass over bare, patched or heavily textured plasterboard is not separated from the lighter finish coat, and no primer or sealer is part of the litre figure.
  • Nothing in the arithmetic allows for paint left in the tray, held in a roller sleeve, or kept back for touch-ups — the litres shown are the surface's bare requirement, and only the cost line rounds anything up, to whole US gallons.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Schematic layout — positions are illustrative, quantities are exact. This calculator is told how many doors and windows there are, never where they sit or how big each one is, so they are drawn evenly spaced at the standard allowance it deducts. Moving one would change nothing in the numbers above.

Plan of Room, 13′ by 11′ 6″, with 1 door(s) and 2 window(s), positions shown schematically.13′11′ 6″1′

Part of bigger jobs

This trade is one line of several job takeoffs. Run the whole job and every other trade comes back with it, off the same measurements.

Or plan the space itself: measure it once, doors and windows included, and this figure comes back worked out on that space, with what goes with it.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-17 · v1.2.1

Regulatory standards & verification citations2
  1. Standard interior door/window opening allowances used by professional estimators (~21 sq ft door, ~15 sq ft window)
  2. Paint coverage rate varies by product — always check your specific paint can's label for its stated coverage per liter/gallon
Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Protection this work requires

  • Stop and check first. Paint under later coats in older housing can be lead-based, and sanding or heat-stripping it produces lead dust that is especially harmful to children and to anyone pregnant. Test before you disturb it — this is a job for a tested, controlled method, not a better mask.

Tools and safety for this job

To roll and cut in two coats, prepare a surface for paint and mist-coat or prime the new surface. Generic types, no brands, no prices.

  • Joint-compound dust is very fine and travels: a P1/FFP1 mask is the minimum, and a damp-sponge finish avoids most of it.
  • A dust mask does nothing about solvent vapour: ventilate through, and use an organic-vapour (A1) cartridge respirator in an enclosed room.
  • Most fatal falls on small jobs are from under three metres: use a tower or a ladder tied at the top, and never work off the top two rungs.
Show the 12 tools this job needs

Essential

  • Brushes

  • Dust sheets and masking

  • Filling knife

  • Roller frame, sleeves and tray

  • Scraper

Recommended

  • Caulking gun

  • Extension pole

  • Mixing bucket or tub

  • Pole sander

  • Random orbital sander

  • Step ladder

Optional

  • Dust extractor or vacuum with a fine filter

Also needed as materials: abrasive discs, caulk and sealant cartridges, masking tape, plastic sheeting, roller sleeves, sanding screens or paper.

what each painting tool is for, and the spec that decides which to buy where one does.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

  • Painting Interior Wallsuses this calculator

    On interior work the substrate sets the numbers: porosity, adhesion and the old colour decide coverage, primer class and coat count.

  • Painting Woodwork and Trimuses this calculator

    Why a white gloss goes ivory behind the door, what a live knot does to a waterborne film, and how a metre of moulding becomes a square metre of paint.

  • Stripping Out a Fit-Out at Lease Enduses this calculator

    A schedule of dilapidations lands eleven weeks before expiry. Which items the consents oblige you to remove, and what the strip-out actually weighs.

Still deciding? Deck Stain vs Deck Paint · Paint vs Wallpaper — the factors that actually differ, with no invented prices.

Already have some? How much wall will my paint cover?

Worked example: Bedroom repaint — step 2 of 7

Worked for these jobs: A bedroom's walls, in litres of paint · A living room repainted, in gallons

Already gone wrong? The paint is peeling off my new plaster · My paint is blistering or bubbling

The data behind it: Production rates by operation

How to calculate paint in 14 steps

  1. Surface to PaintPick how the walls are given: as a room, as a length and height, or as a ready area.
  2. Length of Wall to PaintHow far the painted walls run, measured at skirting level.
  3. Height PaintedSkirting to ceiling, or as high as the paint goes.
  4. Wall Area to PaintThe surface the paint covers before the doors and windows are taken off.
  5. Room LengthThe length of the room, wall to wall.
  6. Room WidthThe width of the room, wall to wall.
  7. Wall HeightFloor-to-ceiling height.
  8. Number of DoorsDoors are not painted with wall paint, so their area is subtracted.
  9. Number of WindowsWindows are not painted with wall paint, so their area is subtracted.
  10. Area of One DoorWhat each door takes off the walls. The default suits a standard interior door with its frame.
  11. Area of One WindowWhat each window takes off the walls. The default suits a typical window.
  12. Number of CoatsMost walls need 2 coats for even, opaque coverage.
  13. Paint CoverageThe area one unit of your specific paint covers — the spread rate printed on the tin.
  14. Read the resultThe tool computes the result from those figures and shows the formula, its sources, and a confidence rating alongside it.

Frequently asked questions

Does this include the ceiling?
No — this calculator estimates wall paint only. Ceilings are typically a different paint (flat white) and should be calculated separately using the room's floor area.
Why subtract door and window area?
You don't paint over doors and windows with wall paint, so their area doesn't count toward how much paint you need.
How many coats do I actually need?
2 coats is standard for most color changes. Going from a dark color to a light one, or painting bare drywall, often needs a 3rd coat.
Where do I find my paint's actual coverage rate?
It's printed on the paint can label, usually as square feet or square meters per gallon/liter. Use that exact figure instead of our 10 m²/L default for the most accurate estimate.
Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.