Paint Coverage Calculator

How much paint does a room take?

The most common DIY painting mistake is buying either too little paint (and having to make an emergency hardware store run mid-project) or too much (wasting $40–$80 in unused product). Getting the calculation right from the start saves both time and money.

The formula is straightforward: calculate your total paintable wall area, subtract deductions for doors and windows, multiply by the number of coats, add a 10% waste buffer, then divide by the coverage rate on the paint can label (typically 350–400 sq ft per gallon). Our calculator does this automatically — enter your room's length, width, and ceiling height, and the tool handles the rest.

For a typical bedroom (12×14 ft, 8-ft ceilings, one door, two windows, two coats), you'll need approximately 2 gallons. A large living room (20×16 ft, 9-ft ceilings, two doors, three windows, two coats) typically needs 4–5 gallons. Hallways and stairwells with high ceilings can surprise you — run the numbers before shopping.

One important nuance: these calculations cover walls only. If you're also painting the ceiling, add a separate calculation for the room's floor area (length × width). Ceilings usually need only one coat if they're already white, or two coats if you're changing the ceiling colour. Trim, baseboards, and doors are calculated separately — they use far less paint and are typically bought in quarts, not gallons.

Paint coverage rates by surface type

Not all surfaces absorb paint equally, and the coverage rate printed on a paint can assumes ideal conditions: a smooth, clean, previously painted surface. Real surfaces vary considerably.

Previously painted smooth walls (standard): 380–420 sq ft per gallon. This is the baseline most DIYers will work with when repainting a room. The existing paint acts as a sealant, and the new paint sits on top without significant absorption. Two coats gives excellent coverage and colour consistency.

Bare or newly patched drywall: 200–300 sq ft per gallon. Bare drywall is highly porous — the paper facing and joint compound soak up paint aggressively. Without primer, the first coat of finish paint disappears into the surface and provides almost no colour coverage. Always prime bare drywall first; it saves paint, improves adhesion, and produces a far better final result.

Textured walls (knockdown, orange peel, popcorn-texture): 300–350 sq ft per gallon. Texture increases the actual surface area being painted — recessed areas catch paint but also absorb more. Use the 15% waste factor in our calculator for textured surfaces, or reduce your assumed coverage rate to 350 sq ft/gallon for more accurate estimates.

Concrete, brick, or masonry: 150–250 sq ft per gallon, depending on porosity. Masonry paints (elastomeric or masonry-specific formulas) are formulated for this purpose and have better coverage than standard interior latex on porous surfaces. If you're painting an interior concrete basement wall, use a masonry sealer as the first coat.

Glossy or semi-gloss surfaces: Standard coverage (~400 sq ft/gal), but adhesion is the concern. Glossy paint creates a non-porous, difficult-to-adhere surface. Lightly sand with 120-grit sandpaper before repainting to dull the sheen and improve bond. Skip this step and your new coat may peel within months.

How many coats of paint do you need?

The number of coats determines how much paint you need — and it's the most commonly underestimated variable in DIY painting projects.

One coat: Appropriate for minor touch-ups, matching an existing colour exactly on a freshly cleaned surface, or when using a high-hide premium paint specifically rated for one-coat coverage. One coat over a significantly different colour will almost always show bleed-through, especially in raking light.

Two coats: The standard for most painting projects. Two coats provide consistent, even colour coverage, improved durability, and better resistance to scuffs and stains than a single coat. For most colour changes on previously painted walls in good condition, two coats of quality paint is the right answer.

Three coats: Required when making dramatic colour changes — particularly reds and yellows, which have notoriously poor hide due to their pigment chemistry. Also necessary when painting a light colour over a dark one without a grey tinted primer coat first. If you've painted two coats and still see the old colour showing through in raking light, a third coat is needed. Having a primer coat (or a grey "cover coat" between the old colour and the new topcoats) often eliminates the need for a third full coat.

Pro tip — tint your primer: When making a dramatic colour change, ask the paint store to tint your primer to a colour approximately halfway between the old wall colour and the new colour. This single technique can eliminate the need for a third coat, saving both paint and labour time. Most stores tint primer for free or a small charge.

Do you need primer? When it's mandatory vs optional

Primer is one of those topics where homeowners often skip it to save a step — and then regret it. Here's a clear breakdown of when it's mandatory, when it's beneficial, and when you can legitimately skip it.

Mandatory primer situations: Bare drywall (including freshly sanded repairs) — primer seals the porous surface and prevents paint absorption. New wood trim — primer is essential for adhesion on bare wood. Stain-blocking situations (water damage rings, smoke, crayon, marker) — use an oil-based or shellac-based stain-blocking primer specifically; standard latex primer won't fully block stains. Painting over fresh joint compound patches — unprimed patches absorb finish coats differently and create visible "holidays" or sheen variation.

Strongly recommended situations: Dark colour to light colour — a grey-tinted primer dramatically reduces the number of topcoats needed. Glossy surfaces — a bonding primer after light sanding improves adhesion. Transitioning between very different paint sheens (gloss to flat, flat to satin) — primer helps create a uniform surface.

When primer can be skipped: Repainting a wall in approximately the same colour or a slightly different shade in the same sheen, where the existing paint is in good condition (no peeling, no stains), and you're using a quality "paint + primer in one" formula. In this scenario, two coats of self-priming paint typically gives equivalent results to a primer plus one topcoat — while saving the additional drying time of a separate primer step.

How to buy paint without overspending

Paint is one of the few home improvement materials where buying the wrong amount is an expensive and frustrating mistake in both directions. Here's how to shop smart.

Buy by the gallon, not the quart: A quart costs roughly $12–$20 and covers about 100 sq ft per coat. A gallon costs $30–$50 and covers 400 sq ft. If you need more than 1.5 quarts, buying a gallon is almost always cheaper per square foot. The only exception: touch-up paint you know you'll rarely use, where a quart is plenty.

Buy all paint from the same batch: Custom colours are mixed by machine, and batches can vary slightly. If you're buying multiple gallons for a single project, have the store mix them all at the same time, or buy slightly more than you need from one batch rather than buying two separate batches at different times. Mixing paint from different cans (a technique called "boxing") ensures consistent colour across the entire surface.

Keep a record: Write the paint brand, colour name, colour code, and sheen on a piece of tape inside the fuse box or on the wall behind an electrical plate. Future touch-ups will match perfectly. Photograph the paint can label on your phone before throwing it away. This information is invaluable when touching up scuffs 2–3 years later.

Don't buy on price alone: Budget-tier paints ($15–$20/gal) typically have lower pigment concentration, poorer hide, and require more coats than mid-range paints ($30–$45/gal). In many cases, buying one gallon of a mid-range paint replaces needing 1.5 gallons of budget paint — making the mid-range option cheaper overall. Premium paints from brands like Benjamin Moore, Sherwin-Williams, and Behr Premium Plus offer the best coverage per coat but come at $55–$80/gal.

Frequently asked questions