Wall Paint Calculator
Estimate paint needed for walls. Adjust coats, coverage, and a waste factor.
Quick guide
- Start with paintable wall area (square feet/meters), or measure walls and subtract big openings.
- Choose a realistic coverage rate and number of coats (texture and color changes matter).
- Add a small buffer for touch-ups, roller/brush waste, and future repairs.
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- If you’re painting ceilings or trim with different products, estimate them separately.
- Treat primer as a separate line item when painting new drywall, stained surfaces, or glossy paint.
- If you’re painting doors, baseboards, or cabinets, estimate those separately—wall area math doesn’t capture them well.
Coverage depends on surface and color
Most paint estimates assume a smooth, previously painted wall. Fresh drywall, heavy texture, porous surfaces, and big color changes can all reduce coverage and increase the number of coats.
If you're switching sheen (e.g., flat to satin) or painting over patches, plan extra for touch-ups and the "extra coat you didn't expect."
Treat primer as its own step: it can improve coverage and durability, but it still requires material and time—especially on repairs and raw drywall.
For accuracy, separate walls, ceilings, and trim. They often use different products and can have different coverage and coat counts.
Coverage is a system, not a single number. The same paint can cover very differently on smooth walls vs orange-peel texture vs fresh joint compound that wasn’t properly primed.
Coats are driven by color and sheen. Deep bases, bright whites, and dramatic color changes often need more coats than the label suggests, especially if you want an even finish with no flashing.
Worked example: a 12' x 14' room with 8' ceilings has wall perimeter 52'. Wall area ≈ 52 x 8 = 416 sq ft. Subtract a 20 sq ft door and a 30 sq ft window for a tighter estimate → 366 sq ft. Two coats at 350 sq ft/gal is ~2.1 gallons; with a buffer and cut-in waste, many people buy 3 gallons or 2 gallons + a quart for touch-ups.
Time and waste scale with edges. Lots of trim, corners, and cut-ins may not change square footage much, but it can increase paint waste and the number of times you reload the brush/roller.
Prep can save paint. Cleaning, sanding glossy surfaces, patching, and caulking reduce failures and rework. Skipping prep often costs more paint later than you saved up front.
Coverage assumptions: smooth walls can align with the label coverage, but porous patches, fresh drywall, and heavy textures often need more product. Use a conservative coverage rate if you’re unsure, or test a small area with the exact paint and roller nap you’ll use.
Coat strategy: decide where to spot-prime vs full-prime, and decide whether a tinted primer or gray primer makes sense for big color changes (project dependent). A good coat strategy often reduces the total number of finish coats needed for an even look.
Ceiling strategy: ceilings often get fewer shadows to hide defects, so uneven coverage can show. If you’re repainting a stained or water-marked ceiling, plan primer and an extra finish coat rather than hoping one coat will cover.
Trim and doors are their own estimate. Enamel trim paints often have different coverage and cure time than wall paint, and door edges can consume more paint than you expect when you do both faces and the edge profiles.
Sheen strategy: higher sheen usually shows surface defects and lap marks more. If you want a smooth semi-gloss on trim, spend more effort on sanding/filling and use the right tool (brush + mini-roller) rather than trying to solve it with extra coats.
If you are painting kitchens and baths, cleaning and degreasing is part of the material plan. A strong cleaner and the right primer can prevent adhesion failure and save you from repainting later.
If you are spraying, overspray and masking can increase material use even when coverage is fast. For many rooms, rolling walls and brushing cut-ins wastes less paint and is easier to control.
Wall Paint Calculator
Estimate paint needed for walls. Adjust coats, coverage, and a waste factor.
Results
- Base gallons (no waste)
- 4.57
- Waste buffer (gallons)
- 0.46
- Estimated gallons
- 5.03
How to measure for paint
- Find wall area (per wall width x height) and add them up.
- Optionally subtract large windows/doors if you want a tighter estimate.
- Choose coats and a coverage rate based on your paint and wall texture.
- If you're unsure about coverage, do a small test area with the exact paint and adjust your estimate before buying everything.
- Estimate ceilings separately as length x width, and estimate trim separately (baseboards/door casing) if it is a different paint.
- If you are painting both sides of doors, remember doors have two faces (and often need extra coats on edges).
Assumptions to double-check
- Textured walls and color changes can reduce coverage.
- Primer can reduce coats, but it doesn't replace paint volume.
- Ceilings and trim often need different paint and coverage assumptions.
- Cut-in work (edges, corners, trim lines) increases time and waste even if area math is correct.
- Repaints over glossy surfaces often need prep and primer; skipping prep can cause failures that waste more paint later.
- Spraying can increase overspray and waste even if it speeds up coverage; rollers typically waste less paint.
- Porous repairs (fresh joint compound, patch spackle) can flash through paint if not primed, creating the illusion you need more coats.
- Coverage rates on labels assume ideal conditions; if you are painting over repairs, stains, or high-contrast colors, plan a lower coverage rate and/or an extra coat for a consistent finish.
Buying tips
- Buy enough from the same batch to avoid color variation.
- Round up if you'll do multiple coats or have a lot of cutting-in.
- Keep a small amount labeled for future touch-ups.
- If you’re doing a major color change, budget primer and a second finish coat more often than not.
- Choose the right roller nap for your wall texture; the wrong nap can reduce coverage and leave a poor finish.
- If color accuracy matters, buy a sample first and check it in your lighting before purchasing gallons.
- If you have multiple rooms, buy enough at once so sheen and tint are consistent across rooms and touch-ups later.
- If you are painting trim/doors/cabinets, budget the correct paint type (enamel) and consider buying a small extra for touch-ups after full cure (nicks happen).
Common mistakes to avoid
- Using footprint area instead of wall area (walls are usually much larger than the floor).
- Forgetting additional coats for deep colors, stains, or dramatic color changes.
- Not budgeting for trim/ceiling paint separately when it's a different product.
- Ignoring primer on patched or stained areas (it can cause flashing and uneven finish).
- Buying the cheapest roller/brush and leaving a poor finish that requires extra coats and touch-ups.
- Skipping cleaning/degreasing in kitchens and bathrooms, then having paint peel and needing a redo.
- Assuming the label coverage is guaranteed on every surface; real coverage varies a lot with texture and porosity.
Paint coverage quick reference (typical)
Use product labels when you have them. This table is a planning reference for common wall paint and primer coverage.
| Product | Typical coverage (per coat) | Notes |
|---|---|---|
| Wall paint | 350–400 sq ft per gallon | Texture/porosity lowers coverage |
| Primer | 250–400 sq ft per gallon | Stains and patches can require extra |
| Ceiling paint | 300–400 sq ft per gallon | Textured ceilings often lower |
| Trim enamel | 350–450 sq ft per gallon | Depends heavily on profile and prep |
- Big color changes, bare drywall, and heavy texture often increase coats.
- Treat walls, ceilings, and trim as separate line items if products differ.
- Round up near thresholds; running short mid-job is expensive.
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Results are estimates for informational purposes only. Always verify measurements and product specifications.