Paint Calculator
Find out exactly how many gallons — and quarts — to buy for a room, a single wall, a ceiling, or the whole outside of a house, with doors, windows, gables and coats accounted for.
8″ is standard; newer homes often 9″.
Counted at 20 sq ft each.
Counted at 15 sq ft each.
One storey ≈ 9–10 ft, two storeys ≈ 18–20 ft. Measure to the eaves — gables are added separately.
The triangles under the roof peak. A simple gable roof has 2; a hip roof has 0.
Siding drinks paint — pick 250–300 sq ft/gal below unless it's smooth and previously painted.
Check your paint can — manufacturers print coverage per gallon on the label.
You need
Enter dimensions
| Detail | Amount |
|---|---|
| Paintable area | — |
| Area × coats | — |
| Buy as | — |
Mid-range interior latex commonly runs $30–$60 per gallon.
What Will This Paint Job Cost?
Paint is the cheap part of painting. On a professional bid it's usually 15–20% of the total — everything else is labor, prep, and materials. Here's what the job costs both ways, using the wall area calculated above.
Better paint covers in fewer coats. Going up a grade often costs less than the extra gallon and extra day a cheap paint needs.
Estimated job cost
Enter dimensions above
| Line item | Amount |
|---|---|
| Paint | — |
| Labor | — |
| Supplies | — |
National ranges for planning and checking a quote — not a bid. Heavy prep, high ceilings, and dark-over-light color changes all push a real quote up.
What painters charge in 2026
| How it's priced | Typical range | Notes |
|---|---|---|
| Per square foot of wall | $1.50–5.50 | The number most contractors actually bid from |
| Per room | $300–1,000 | National average lands near $625 a room |
| Per hour | $20–50 | Common for small jobs and touch-ups |
| Whole interior, 1,500–2,000 sq ft home | $3,000–8,000 | Walls, ceilings, trim |
Why quotes vary so much on the same room
Labor is 70–95% of a painting bid. That's why two quotes on an identical room can differ by hundreds of dollars — you're pricing crews and prep standards, not paint.
- Prep is the whole game. Filling nail holes, sanding, caulking gaps, and priming patches can double the hours on a wall that looks fine from the doorway. A cheap bid often means less prep, and that shows within a year.
- Ceiling height changes everything. Above 9 feet means ladders or scaffolding, slower cutting-in, and a higher rate per square foot.
- Dark to light needs an extra coat — sometimes two, plus a tinted primer. Tell whoever's quoting what color is on the wall now, not just what you want.
- Trim and doors are priced separately by most painters and are slow, detailed work. A "room" quote may be walls only — ask.
- Watch the square footage they're quoting. Painters price wall area, which at an 8-foot ceiling is roughly 2.8× the floor area. A quote that sounds cheap per square foot may be using floor area.
How to Calculate Paint
Paint is bought by coverage — how many square feet one gallon covers per coat. The math is three steps for any surface:
- Find the paintable area. For a whole room, that's the perimeter × ceiling height; for one wall, width × height; for a ceiling, length × width. Subtract about 20 sq ft per door and 15 sq ft per window.
- Multiply by coats. Two coats means the paint has to cover the area twice.
- Divide by coverage. Typical interior latex covers about 350 sq ft per gallon on a normal wall — less on rough or bare surfaces.
Paint formulas
Room walls: area = 2 × (length + width) × height − openings
Gallons = (area × coats) ÷ coverage per gallon
Worked example — 12 × 12 room, 8″ ceilings, 1 door, 1 window, 2 coats: perimeter 48 ft × 8 ft = 384 sq ft − 35 sq ft of openings = 349 sq ft. × 2 coats = 698 sq ft ÷ 350 = 2.0 gallons.
Paint Needed for Common Room Sizes
Two coats on walls, 8 ft ceilings, one door and one window subtracted, 350 sq ft/gal coverage:
| Room size | Wall area | Gallons (2 coats) | Buy |
|---|---|---|---|
| 10 × 10 ft | 285 sq ft | 1.6 | 1 gal + 3 qt |
| 12 × 12 ft | 349 sq ft | 2.0 | 2 gallons |
| 12 × 16 ft | 413 sq ft | 2.4 | 2 gal + 2 qt |
| 16 × 20 ft | 541 sq ft | 3.1 | 3 gal + 1 qt |
| 20 × 20 ft | 605 sq ft | 3.5 | 3 gal + 2 qt |
Painting the Outside of a House
Exterior estimating goes wrong in two predictable places, and the calculator handles both.
Gables are the missed area. Most people measure the walls, forget the triangles under the roof peak, and come up short. Each gable is ½ × span × rise. On a 28 ft-wide house with a 7 ft rise that's 98 sq ft per end — nearly 200 sq ft across two gables, which is most of a gallon at two coats. A hip roof has no gables at all; set the count to zero.
Siding drinks more paint than drywall. Interior walls give you 350–400 sq ft per gallon. Rough cedar, stucco, fibre cement and anything bare or chalky pull that down to 250 or less, and the textured surface is physically larger than its measured footprint. If you're unsure, choose the lower coverage figure — running out mid-wall on an exterior means a visible lap mark, not just another trip to the store.
Worked example: a 40 × 28 ft single-storey house with 9 ft walls, two gables at 7 ft rise, two doors and twelve windows works out to 1,200 sq ft of paintable surface — 6.9 gallons at two coats and 350 sq ft/gal. Drop the coverage to 250 for rough siding and the same house needs 9.6 gallons.
Trim, doors and shutters are usually a different colour and product, so measure them separately rather than trying to net them out — the calculator already subtracts door and window openings from the wall area.
Tips Before You Buy
- Buy all the paint at once. Cans tinted in separate batches can vary slightly — or "box" them by mixing cans together before starting.
- Dark over light needs primer. A tinted primer coat is cheaper than a third coat of finish paint.
- Keep the leftover. Sealed in the original can, leftover paint is your color-matched touch-up supply for years.
- Ceilings use flat, walls use eggshell or satin. Different sheens hide and wash differently — the calculator works for any of them.
Frequently Asked Questions
How much paint do I need for a 12×12 room?
About 2 gallons for two coats on the walls (349 sq ft after subtracting a door and window at 350 sq ft/gal coverage). Add a gallon of ceiling paint if the ceiling is included.
How many square feet does a gallon cover?
350–400 sq ft per coat on smooth, previously painted surfaces; 250–300 on rough, textured, or bare surfaces. The can's label states the manufacturer's figure.
Do I really need two coats?
For uniform color and warranty coverage, yes. One coat only works when repainting the same color and sheen. Drastic changes may need primer plus two coats.
Should I subtract doors and windows?
Yes — about 20 sq ft per door and 15 per window. For a single small window, many painters skip the subtraction and keep the extra as touch-up.
How much ceiling paint for a 12×12 room?
144 sq ft — one coat takes about 0.4 gallons, so a single gallon handles two coats.
Quart or round up to a gallon?
A gallon costs about twice a quart's price for four times the paint. Within a quart of the next gallon? Round up and keep the remainder for touch-ups.
How much paint to paint the outside of a house?
A typical 40 × 28 ft single-storey house with 9 ft walls and two gables is about 1,200 sq ft — roughly 7 gallons for two coats on smooth siding, or 9–10 on rough siding at 250 sq ft/gal.
Do I include the gables?
Yes, and it's the most common omission. Each gable is ½ × span × rise — often close to 100 sq ft per end. A hip roof has none.
Why did I run short even though the can said 400 sq ft/gallon?
That figure assumes a smooth, previously-painted wall. Textured walls and bare drywall are porous and can drop real coverage to 250–300 sq ft per gallon — which is why this calculator lets you set your own coverage rate instead of locking in the can's number.
Do I need primer?
Yes when you're covering a dark or stained color, painting bare drywall, or making a drastic sheen change — skip it on a same-color repaint. Primer isn't included in the topcoat gallons above, so budget it as a separate coat when any of those apply.
How much extra should I buy for touch-ups?
Round up to the next full gallon rather than buying the exact math. A partial gallon left over is normal — and worth keeping, since a later remix from the same can rarely matches the original exactly.
How much does it cost to paint a room?
$300–1,000 professionally, averaging around $625. DIY is usually $80–250 for a normal bedroom — paint plus supplies.
How much do painters charge per square foot?
$1.50–5.50 per square foot of wall surface. Note that's wall area, not floor area — at an 8 ft ceiling, walls are about 2.8× the floor.
Why is professional painting so expensive?
Labor is 70–95% of the bid; paint is only 15–20%. You're paying for prep hours — patching, sanding, caulking, masking — which is also what makes the finish last.
References
- Sherwin-Williams — paint coverage and estimating guidance: sherwin-williams.com
- Benjamin Moore — product data sheets (spread rate per gallon): benjaminmoore.com
- PPG — how much paint do I need: ppgpaints.com
Embed This Calculator
Run a blog, a supplier site, or a class page? You're welcome to put this calculator on your own site — free, no signup, no API key. Copy the snippet, paste it into your HTML, done.
The only condition: keep the “Powered by MeasureQuik” link visible. It's how we keep the calculators free. Full details on the embed page.