Paint Calculator — How Much Paint Do I Need?
Work out exactly how much paint your project needs: walls, ceilings, trim and skirting, interior doors, kitchen cabinets and fences — across multiple rooms, with primer logic, metric or imperial units, a can-size optimizer and a cost estimator. Free, no signup, private.
100% client-side — your data never leaves your browserCalculate your paint
Results
Cans to buy
| Can size | Qty | Subtotal | Price used |
|---|
Per-room breakdown
| Room | Walls | Ceiling | Trim | Doors | Paint |
|---|
What you can calculate
Looking for a paint calculator for UK homes? This one works in the UK, US, Canada, Australia and NZ — metric or imperial. Popular uses:
- Walls by room size — a paint calculator by room size for painting a whole house (a whole-house paint calculator): add each bedroom, living room, kitchen or bathroom with its own dimensions, doors and windows. How much paint for bedroom walls? A 4×5 m bedroom (walls, two coats) needs about 9 liters — try the presets above.
- Ceilings — use it as a ceiling paint calculator; flat paint recommended to hide imperfections.
- Trim, skirting and doors — the paint calculator trim and doors mode estimates skirting from the room perimeter and counts both sides of every interior door. Use gloss paint here.
- Kitchen cabinets — a kitchen paint calculator and paint calculator for cabinets: enter total cabinet front area, with primer plus a durable satin finish.
- Fences and decks — a fence paint calculator (also a deck paint calculator): how much paint for fence panels? Enter length × height and pick one or two sides.
- Exterior and garage — an exterior paint calculator that doubles as a garage paint calculator: add each exterior wall as a room, and use exterior-grade paint with primer on bare wood.
- Interior repaints — an interior paint calculator for refreshes: one coat is often enough for same-color walls in good shape.
- Cost — the paint calculator cost estimator totals can prices across the whole project.
- Coverage & primer — set the paint calculator coverage rate to match your can, and the paint calculator primer logic adds one primer coat on bare surfaces. Unsure how many coats? The paint calculator's how-many-coats setting defaults to two, the standard for interior walls.
How the paint calculation formula works
The calculator applies the standard paint formula room by room:
- Wall area = 2 × (length + width) × height, minus door and window openings.
- Add surfaces: ceiling (length × width), trim (perimeter × 10 cm), doors (both sides), plus cabinets and fence.
- Multiply by coats (and +15% for textured surfaces).
- Divide by coverage (default 10 m²/L or 350 sq ft/gal per coat) — this gives the total paint amount in liters or gallons.
- Primer: one extra coat at the same coverage when the surface is bare.
- Cans: the optimizer picks the can-size mix with the least leftover paint.
Coverage guide
| Surface | Typical coverage | Notes |
|---|---|---|
| Smooth interior walls | 10 m²/L · 350 sq ft/gal | Default in the calculator |
| Ceilings | 10 m²/L · 350 sq ft/gal | Use flat/matt paint |
| Textured / rough walls | ~8.5 m²/L · ~300 sq ft/gal | Tick “textured surface” (+15%) |
| Trim, skirting, doors | 10 m²/L · 350 sq ft/gal | Semi-gloss recommended; small areas — buy the smallest can |
| Bare drywall / wood (primer) | 10 m²/L · 350 sq ft/gal | One coat of primer before topcoats |
| Fence / exterior wood | 8–10 m²/L | Use exterior-grade paint or stain |
Do you need primer?
- Yes — new drywall, bare wood, fresh plaster, new masonry, or drastic color changes.
- Usually no — previously painted walls in good condition getting a similar color.
- Dark to light — use a tinted primer or add an extra topcoat (the calculator's “dark color” option does the latter).
Tips to avoid buying too much (or too little)
- Measure twice: the biggest error is guessing room dimensions.
- Don't forget the second coat — most “one-coat” disappointments are really two-coat jobs.
- Buy ~10% extra for touch-ups; “box” (mix) multiple cans for color consistency.
- Trim and doors use little paint — one small can usually covers a whole house's trim.
- Keep the lid-on leftovers labeled per room for future repairs.
Frequently asked questions
How much paint do I need for a 12x12 room?
For a 12×12 ft room with 8 ft ceilings, one door and one window, two coats on the walls need about 696 sq ft of coverage — just under 2 gallons at 350 sq ft per gallon. Add the ceiling (144 sq ft, two coats) and you need about 3 gallons total. Enter your exact dimensions above for a precise answer.
How do I calculate how much paint I need?
Use the paint calculation formula: (paintable area − doors − windows) × coats ÷ coverage. Example: 45 m² of wall, 2 coats, 10 m² per liter = 9 liters. The calculator above applies this per room and adds primer, ceiling, trim and extras automatically.
How many coats of paint do I need?
Two coats is the standard for interior walls — better color depth and durability. One coat is fine for a same-color refresh on walls in good shape. Going from dark to light usually needs a third coat or a tinted primer.
Do I need primer before painting?
On bare surfaces — new drywall, bare wood, fresh plaster, new masonry — yes, one coat of primer. Previously painted walls in good condition usually don't need it. Select “bare / unpainted surface” in the calculator to add primer automatically.
How much area does one gallon or one liter of paint cover?
The common rule of thumb is 350–400 sq ft per gallon (about 9–10 m² per liter) per coat on smooth walls. Textured or porous surfaces can drop that by 15% or more — the calculator has a textured-surface option for this. Always check your paint can's stated coverage.
How do I account for doors and windows?
Subtract each opening: a standard interior door is about 21 sq ft (1.9 m²), a typical window about 15 sq ft (1.7 m²). The calculator subtracts these automatically from the number of doors and windows you enter per room.
How much paint do I need for the ceiling?
Ceiling area is length × width. A 4×5 m room has 20 m² of ceiling; two coats at 10 m² per liter need 4 liters of ceiling paint. Use flat/matt ceiling paint to hide imperfections, and tick the ceiling option above.
How much paint do I need for a fence?
Measure length × height and pick one or two sides. A 20 m long, 1.8 m high fence painted both sides is 72 m²; two coats at 10 m² per liter need about 14.4 liters. Use exterior-grade paint or stain for fences.
How much paint do I need for kitchen cabinets?
Estimate the total front area of cabinet doors and drawer fronts and enter it in the cabinets field. Cabinets almost always need primer plus two coats of durable satin or semi-gloss paint.
What about trim, skirting boards and interior doors?
Trim/skirting is estimated from the room perimeter × 10 cm height; interior doors count both sides. Semi-gloss or gloss paint is best for trim and doors — it resists scuffs and wipes clean.
Can I use this paint calculator for exterior walls, a deck or a garage?
Yes. Add each exterior wall as a room (or use fence mode for long runs). Exterior and deck surfaces need exterior-grade paint, and bare wood needs primer. A deck floor works like the fence calculation: length × width, two coats.
Do textured walls need more paint?
Yes — roughly 15% more than smooth walls, because texture increases the real surface area and absorbs more paint. Tick the textured-surface option to add the allowance automatically.
How much does it cost to paint a room?
Enter each can size's price in the cost section and the calculator totals it. As a rough guide, a 4×5 m bedroom (walls, two coats, mid-range paint) typically needs one 10-liter can — plus primer if the walls are bare.
Does the calculator work in liters and gallons?
Yes. Metric mode uses meters, square meters and liters (default 10 m²/L). Imperial mode uses feet, square feet and gallons (default 350 sq ft/gal). Can sizes switch too: 10 / 4 / 2.5 / 1 L, or 5 / 1 gal plus quarts.
Is my data private?
Yes. This paint calculator runs 100% in your browser — your room dimensions and prices are never sent to any server.
Can I paint over a dark color with a light color?
You can, but plan for an extra coat since dark colors show through. Tick “painting over a dark color” to add a third coat, or apply a tinted primer close to your topcoat color first.