Paint Calculator
Calculate the paintable surface area, required paint quantity, and costs for your painting project. Get accurate calculations for walls and ceiling separately, including material costs and labor fees.
Accurate Paint Quantity and Cost Calculation
Our paint calculator helps you determine the exact amount of paint needed for your project, including separate calculations for walls and ceiling. Simply enter your room dimensions, number of layers, and paint coverage rate. The calculator will provide you with detailed material requirements and cost estimates, including paint costs and labor fees. All calculations include a safety margin to ensure you have enough paint for your project.
Results
WALL
CEILING
Cost Breakdown
How to Estimate Paint for a Room
A gallon of paint covers roughly 350 to 400 square feet on a smooth, previously painted surface. Divide your wall area by 350, multiply by the number of coats, and you have the answer. New drywall, bare wood and a dark-to-light colour change all move that number, which is where most under-ordering comes from.
1. Measure the paintable walls
Perimeter times ceiling height. A 16 by 12 room with 8 foot ceilings gives 448 square feet.
2. Subtract doors and windows properly
A standard door is about 21 square feet and an average window about 15. Unlike drywall, subtract these — you are not cutting sheets, so the area you do not paint is genuinely paint you do not buy.
3. Decide coats before you divide
Two coats is standard. Three if you are going light over dark, or covering a strong colour. New drywall needs primer first, and primer counts as its own coat of material.
4. Divide by coverage
400 square feet of wall, two coats, at 350 square feet per gallon is 2.3 gallons, so three gallons or a five-gallon bucket depending on price.
5. Add ceilings and trim separately
Ceiling paint is a different product and usually a different sheen. Trim is measured in linear feet, not square feet, and a quart covers a lot of it.
6. Round to the container, not to the gallon
Paint comes in quarts, gallons and five-gallon buckets, and a bucket is cheaper per gallon than five separate cans. Anything over about three gallons of one colour is usually a bucket. It also matters for consistency: one bucket is one batch, so there is no slight shade difference between cans halfway along a long wall.
7. Count the colours, not just the area
A house painted in one colour and the same house painted in four are the same square footage and completely different orders — four part-used containers, four cut-in operations, and more masking than painting. When a customer asks why the quote went up after they picked their colours, this is the answer.
Worked Example: a 16 x 12 Bedroom, Walls Only
8 foot ceilings, one door, two windows, repainting an existing mid-tone colour with a similar mid-tone. Two coats, no primer.
| Item | Working | Result |
|---|---|---|
| Wall area | 56 ft perimeter x 8 ft | 448 sq ft |
| Door | 1 x 21 sq ft | −21 sq ft |
| Windows | 2 x 15 sq ft | −30 sq ft |
| Paintable area | 448 − 51 | 397 sq ft |
| Two coats | 397 x 2 | 794 sq ft of coverage needed |
| Gallons at 350 sq ft | 794 ÷ 350 | 2.3 → 3 gallons |
Worked Example: a Whole 1,600 sq ft House Interior
Eight rooms and a hallway, 8 foot ceilings, walls in one colour and ceilings in flat white, all trim in semi-gloss. This is the estimate that goes wrong, because wall area on a whole house is roughly two and a half times the floor area — not equal to it.
| Item | Working | Result |
|---|---|---|
| Wall area rule of thumb | 1,600 sq ft floor x 2.5 | ~4,000 sq ft of wall |
| Less doors and windows | Roughly 12% on an average plan | ~3,520 sq ft paintable |
| Walls, two coats | 3,520 x 2 ÷ 350 | 20.1 → 21 gallons (4 buckets + 1) |
| Ceilings, one coat | 1,600 ÷ 350 | 4.6 → 5 gallons |
| Trim and doors | Measured separately, in linear feet | 3–4 gallons semi-gloss |
| Primer for patches only | Spot priming | 1 gallon |
| Total order | — | ~30 gallons across three products |
Coverage by Surface
Square feet per gallon, per coat. The range is real — check the can for the product.
| Surface | Coverage per gallon | Note |
|---|---|---|
| Smooth, previously painted drywall | 350–400 sq ft | The number most estimates assume. |
| New drywall, primed | 300–350 sq ft | Prime first or the first coat disappears. |
| Textured walls | 250–300 sq ft | Knockdown and orange peel drink paint. |
| Bare wood | 200–300 sq ft | Varies enormously by species and grain. |
| Smooth exterior siding | 300–400 sq ft | Rough or weathered siding much less. |
| Rough or weathered siding | 200–250 sq ft | Cedar shakes and old wood are the worst case. |
| Stucco and masonry | 150–250 sq ft | Texture depth decides it; a first coat can be half the second. |
| Primer on bare drywall | 200–300 sq ft | Drywall primer is meant to be absorbed. |
Paint for Common Room Sizes
Walls only, 8 foot ceilings, one door and two windows deducted, two coats at 350 square feet per gallon. Ceilings are listed separately because they are almost always a different product.
| Room | Paintable walls | Two coats | Ceiling, one coat |
|---|---|---|---|
| 8 x 10 bedroom | ~237 sq ft | 1.4 → 2 gal | 0.2 gal |
| 10 x 12 bedroom | ~301 sq ft | 1.7 → 2 gal | 0.3 gal |
| 12 x 12 room | ~333 sq ft | 1.9 → 2 gal | 0.4 gal |
| 12 x 16 living room | ~397 sq ft | 2.3 → 3 gal | 0.5 gal |
| 16 x 20 great room | ~525 sq ft | 3.0 → 3 gal (or 1 bucket) | 0.9 gal |
| 5 x 8 bathroom | ~157 sq ft | 0.9 → 1 gal | 0.1 gal |
| Stairwell + hallway | Measure it — the height is not 8 ft | Price the access, not the area | — |
What Interior and Exterior Painting Cost
Paint is the small half. On a typical repaint the material is a minority of the invoice and the preparation decides the rest, which is why two honest quotes for the same rooms can differ by a factor of two. The gallons come out of the calculator above. The hours come out of the condition of what you are painting, and that is the number to build the quote around.
How many coats the colour change forces
The same colour over a sound surface can be one coat. Light over dark, or any strong colour, is a primer plus two, which is three passes over every square foot instead of one. Ask what colour is going on before you price anything.
The condition of the surface
Filling nail holes is minutes. Skimming a wall someone has already patched badly, sanding out brush ridges from the last job, caulking the gaps at the trim and priming the stains is where interior painting time actually goes. Walk the rooms and count the repairs rather than pricing from the square footage.
Trim, doors and ceilings
Trim is slow work measured in linear feet, and a room with panelled doors, deep skirting and a picture rail can take longer than its walls. Ceilings need a different sheen, more masking and more time under the roller.
Masking and protection
In an occupied house with furniture, floors and fittings to protect, covering up and putting back is real hours that produce nothing visible. An empty house is a different quote.
Porosity, which the coverage rate on the tin assumes away
The spread rate printed on the tin is measured on a sealed, smooth surface. New drywall, bare plaster, render and old chalky exterior paint drink the first coat, and heavy texture increases the true surface area well beyond the measured wall. That is what the primer coat is for, and it is why the calculator asks for the surface type.
Height and access, especially outside
Everything above ladder height brings scaffolding or a lift, which is a hire cost, a setup day and a takedown day. Two-storey exterior work and stairwell walls are priced on access before they are priced on area.
What exterior work adds
Washing, scraping, sanding back failed paint, spot-priming bare wood, replacing rotten trim, caulking, and a weather window that can stop the job for a week. On an exterior repaint the preparation is usually the majority of the labour, and it is the whole reason one job lasts twelve years and another peels in three.
The Lines Behind a Painting Price
Price the labour lines by the hour against what you find on the walk-round, not as a percentage of the paint.
| Line item | What drives it |
|---|---|
| Paint | Gallons from the area, coats and spread rate, at your trade price |
| Primer and sealer | Bare, patched, stained or porous surfaces, and any strong colour change |
| Fillers, caulk and abrasives | The number of repairs, not the size of the room |
| Masking and protection | Furniture, floors, fittings, and whether the house is occupied |
| Preparation labour | Washing, scraping, filling, sanding, caulking. The biggest line on most repaints. |
| Application labour | Coats x area, plus trim by the linear foot and ceilings counted separately |
| Access | Ladders, towers, scaffolding or a lift, plus the days to set up and strike |
| Sundries and disposal | Rollers, brushes, tape, sheets, and getting the old paint away legally |
The Parts of a Paint Estimate That Are Not Paint
On most interior repaints the material is the smaller half of the number. These are the items that decide whether the job was profitable, and they are the ones a customer comparing two quotes never sees.
Sheen is a separate decision from colour
Flat on ceilings, matte or eggshell on walls, satin in a bathroom or kitchen, semi-gloss on trim and doors. That is three or four different products on one job even in a single colour, and each one is bought in its own container. It also affects coverage — higher sheens tend to go slightly further and show every defect underneath.
Dark colours and colour changes cost coats
Deep reds, strong blues and yellows are pigment-heavy and thin-bodied; three coats over a tinted primer is normal rather than exceptional. Going light over dark is the same problem in reverse. Both are decided by the customer after the quote, so it is worth saying which colours carry a surcharge before they choose.
Prep is where the hours are
Filling, sanding, caulking, degreasing a kitchen, scraping an exterior, taping and masking. None of it appears in a square-footage calculation and all of it is billable time. An estimate that only counts paint loses money on the first house with plaster cracks.
Primer is a product, not a favour
New drywall, bare wood, water stains, patched areas and any strong colour change all need it. Drywall primer is designed to soak in, so it covers less per gallon than finish paint — 200 to 300 square feet is realistic.
Exterior work is measured differently
Siding is walls, but there are also soffits, fascia, gutters, railings, shutters and a front door, all in different products and different sheens. Exterior coverage also drops sharply on weathered wood, and a first coat on bare cedar can take twice what the can claims.
Buy one container more than you calculated
Not as waste — as the touch-up can. A quart of the exact batch left with the customer is worth more in goodwill than it costs, and it is the cheapest way to avoid a return visit for a scuffed corner.
Where Estimates Go Wrong
Estimating one coat because the paint says one-coat
It rarely is, and finding out halfway across a wall costs a trip to the store and a visible lap mark.
Treating textured walls like smooth ones
Texture can cut coverage by a third. Estimating a knockdown ceiling at 400 square feet a gallon leaves you short every time.
Forgetting primer is material too
New drywall, patches and any strong colour change need it, and it has to be bought and carried like anything else.
Using floor area as wall area
On a whole house the walls are roughly two and a half times the floor area. Quoting 1,600 square feet of paint for a 1,600 square foot house is a third of what the job needs, and it is the most expensive arithmetic mistake on this page.
Estimating a stairwell from the plan
A two-storey stairwell wall is not 8 feet high, and the top third of it can only be reached from a ladder or scaffold. The square footage is modest and the hours are not — price the access separately or that room eats the profit from the rest of the house.
Quoting before the colours are chosen
Number of colours, depth of colour and direction of change all move the material and the coats. A quote given on area alone gets revised upwards after the customer has already decided what they are paying, which is the worst moment to have that conversation.
Paint Calculator — Common Questions
What does interior painting cost?
The paint is the small half of it. The number is set by how many coats the colour change forces, how much filling, sanding and caulking the walls need first, how much trim there is, and whether the house is occupied and has to be masked and put back every day. Two honest quotes for the same rooms can differ by a factor of two, and the difference is almost always the preparation rather than the paint.
How much paint do I need for a 12x12 room?
With 8 foot ceilings and normal openings, about 333 square feet of paintable wall. Two coats is 666 square feet of coverage, so two gallons on a smooth like-for-like repaint and three if the walls are textured or the colour is changing.
How many square feet does a gallon of paint cover?
Roughly 350 to 400 on smooth previously painted walls, less on texture, new drywall or bare wood.
How much paint for a whole house interior?
Start from wall area, not floor area — on a typical plan the walls are about two and a half times the floor square footage. A 1,600 square foot house works out near 3,500 square feet of paintable wall, so around 21 gallons for two coats, plus about 5 for the ceilings and 3 to 4 for trim.
Do I subtract windows and doors when estimating paint?
Yes. Unlike sheet goods there are no offcuts, so area you do not paint is paint you do not buy. Use about 21 square feet per door and 15 per average window.
How many coats of paint do I need?
Two on a like-for-like repaint. Three going light over dark. New drywall wants primer plus two.
Is a five-gallon bucket cheaper than five gallon cans?
Almost always, per gallon, and it gives you one batch instead of five so there is no shade variation partway along a wall. It is worth switching to buckets at anything over about three gallons of a single colour.
How much does it cost to paint a room?
Material is the smaller half. Take your gallons, price them at what your supplier charges you for the product and sheen you actually use, then add prep hours, masking, primer where it is needed, and painting hours at your own rate. The calculator above asks for your prices rather than assuming an average, because paint pricing varies more by product line than by region.
Why did my paint quote go up after I picked the colours?
Because the number of colours and their depth change both the material and the number of coats. Four colours means four part-used containers and four cut-in operations on the same square footage, and a deep saturated colour can need three coats over a tinted primer where an off-white needs two.
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Open the calculator →Put This Calculator on Your Site
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