The Paint Calculator That Tells You Exactly How Much to Buy
Enter your room dimensions, number of coats, and finish type. Get the exact gallons needed — down to the quarter gallon. No overbuying. No mid-project hardware store panic.
Which Paint Finish for Every Room
The finish you choose affects how much paint you need, how easy it is to clean, and how the room looks in different light. This is the decision most people get wrong.
Paint Coverage Reference Chart
Standard coverage rates per gallon by finish type
| Paint Finish | Coverage per Gallon | Coats Needed | Best Surface |
|---|---|---|---|
| Flat / Matte Ceiling | 350–400 sq ft | 1–2 coats | Ceilings, textured walls, bedrooms |
| Eggshell Most Popular | 300–350 sq ft | 2 coats | Living areas, bedrooms, dining rooms |
| Satin | 300–350 sq ft | 2 coats | Kitchens, baths, high-traffic areas |
| Semi-Gloss Trim | 250–300 sq ft | 2–3 coats | Trim, doors, cabinets, window frames |
| High-Gloss | 250–300 sq ft | 2–3 coats | Furniture, doors, accent pieces |
| Primer | 200–300 sq ft | 1 coat | New drywall, dramatic colour changes |
Paint Buying Mistakes to Avoid
Not accounting for doors and windows
A standard door is ~20 sq ft, a typical window ~15 sq ft. Two doors and three windows = ~85 sq ft you're over-calculating — about half a gallon wasted.
Not buying extra for touch-ups
Always buy 10% more than calculated. Running out mid-project and getting a new batch risks a colour mismatch even with the same code.
Skipping primer on dramatic colour changes
Going dark to light without primer means 3–4 topcoats instead of 2. One coat of primer plus 2 coats of topcoat is faster and cheaper.
Buying by price instead of coverage rate
Cheap paint often covers 250 sq ft/gal. Premium paint often covers 400+ sq ft. Calculate cost-per-square-foot, not cost-per-gallon.
What to Do Before You Paint
Always buy a sample first
Paint a 12×12 inch swatch directly on the wall and observe it at morning light, midday, and under artificial light at night. Colours behave completely differently under different light sources.
How surface type affects coverage
- New drywall is highly porous — always prime first or plan for an extra coat.
- Previously painted walls in good condition take paint predictably.
- Textured walls have more surface area than they appear — add 10–15% to your amount.
- Bare wood requires priming — raw wood absorbs the first coat almost entirely.
Storing leftover paint
Write the room name and paint code on the lid. Seal tightly, store in a cool dry place away from freezing. Latex paint lasts 2–5 years, oil-based up to 15 years when stored properly.