Paint Calculator
Enter room dimensions, number of doors and windows, and coats to instantly see gallons, quarts, and liters of paint required.
How to use Paint Calculator
The paint calculator estimates litres or gallons of paint required for walls, ceilings, trim or an entire room based on dimensions, number of coats and paint coverage rate. It subtracts door and window area automatically and adds a recommended overage so you have enough for touch-ups without ordering a second tin.
- Enter room dimensions (length, width, ceiling height).
- Enter the number of doors and windows to subtract.
- Set the coverage rate of your chosen paint (shown on the tin).
- Choose the number of coats.
- Review litres or gallons needed, plus recommended purchase quantity.
Your data never leaves your device — 100% private processing.
Paint coverage and coats
Premium paints cover 350–400 sq ft per gallon; budget paints 300–350 sq ft. Two coats are standard for a colour change; one coat works for touch-ups or same-colour repaints. The formula: gallons = total area ÷ coverage rate × coats. Always buy in round-up increments (quart, gallon) — leftover paint is useful for touch-ups for years.
| Finish | Coverage (sq ft/gal) | Best used for | Washability |
|---|---|---|---|
| Flat / matte | 350–400 | Ceilings, low-traffic walls | Low |
| Eggshell | 330–380 | Living rooms, bedrooms | Moderate |
| Satin | 300–360 | Kitchens, bathrooms, trim | Good |
| Semi-gloss | 300–350 | Trim, doors, cabinets | Very good |
| Gloss | 280–330 | Doors, furniture, metal | Excellent |
Surface preparation — the most important step
Paint adhesion and finish quality depend almost entirely on preparation: fill holes and cracks with spackle, sand rough surfaces, clean off grease with TSP solution, and prime bare drywall or repaired spots before painting. Skipping primer on new or repaired drywall leads to uneven sheen and poor adhesion. On dark or stained surfaces, a stain-blocking primer prevents bleed-through.
Glossary
- Sheen
- The reflectivity/gloss level of a paint finish, ranging from flat to high-gloss.
- Coverage rate
- Square feet a gallon of paint covers at the recommended film thickness.
- Primer
- A base coat applied before paint to improve adhesion and hide stains.
- TSP
- Trisodium phosphate — a heavy-duty cleaner for degreasing walls before painting.
Related reading
Frequently Asked Questions
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Why use Paint Calculator?
- Accurate material estimates reduce waste and over-ordering
- Supports both metric and imperial measurements
- Covers common materials: concrete, lumber, flooring, paint
- Results include waste factor buffers for professional accuracy
Common use cases
- Calculate concrete needed for a driveway
- Estimate flooring tiles for a room renovation
- Work out paint quantity for interior walls
- Calculate lumber needs for a deck project
- Estimate roofing material for a pitched roof
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