Paint Calculator
Plan your paint job with confidence—estimate coverage for walls, ceilings, and trim without guesswork. This tool converts room dimensions into total surface area, subtracts doors and windows, and shows how many gallons (and quarts) you’ll need based on your coat count and coverage rate. It’s handy for budgeting, scheduling, and avoiding last-minute store runs or leftover cans.
The Paint Calculator lets you model multiple rooms, choose one or two coats (plus optional primer), set your paint’s coverage, include or exclude ceilings and trim, and add a small waste buffer. The goal is a precise, shareable materials list and cost estimate so you buy the right amount the first time and get a consistent finish. Enter your measurements below to get started.
Calculate how many gallons of paint you need — with deductions, coats, coverage per gallon, and waste allowance.
Your project
Paint totals
How our Paint Calculator works
Formulas, steps & assumptions
Openings: we subtract 21 ft²/door and 12 ft²/window by default.
Coverage: manufacturer labels vary by paint and surface; adjust to match your can.
Waste: covers cut-in, roller load, texture, and touch-ups. Increase for rough walls or dark color over light.
Limitations: vaulted ceilings, stairwells, trim/doors, and highly textured walls require separate takeoffs.
Results interpretation: who this helps
- Homeowners: quick budget check before heading to the store.
- Contractors: fast bid quantities with an explicit waste buffer.
- Property managers: predictable touch-up and repaint planning.
Use cases & examples
Example 1 — Bedroom refresh: 12×14 ft, 8 ft walls, 1 door, 2 windows, 2 coats, coverage 350, ceiling on, 10% waste → typically about 2 gal.
Example 2 — Living room accent wall: 18×0 ft (single wall), 9 ft height, 0 openings, 2 coats, coverage 400, ceiling off, 5% waste → compute wall area 18×9 = 162 ft²; ×2 coats = 324; ×1.05 = 340.2; ÷400 = 0.85 gal → buy 1 gal.
Example 3 — Whole room, ceiling off: 15×12 ft, 9 ft walls, 1 door, 2 windows, 1 coat primer + 1 coat color (run twice or set coats=2), coverage 300 for primer, 350 for color → run both and sum results.
Paint Calculator — FAQ
How many square feet does a gallon of paint cover?
Most interior wall paints cover about 300–400 ft² per gallon on smooth, primed walls. Adjust coverage to match your can and surface.
Do I count doors and windows?
Yes. We subtract a standard area per door (≈21 ft²) and window (≈12 ft²). If yours differ significantly, adjust with the coverage or waste buffer.
Should I include the ceiling?
Check the 'Include ceiling' option to add L×W to the area. Tray ceilings or vaults require separate measurements.
How many coats do I need?
Two finish coats are common for best color depth. If changing from dark to light (or vice versa), consider a primer coat as well.
What waste percentage should I use?
We default to 10%. Increase for rough surfaces, heavy texture, or extensive cut-in; reduce for small touch-ups.
Gallons vs quarts — how do I buy?
We show exact gallons and round up to the nearest quart for purchase planning so you won’t run short mid-wall.
Does sheen affect coverage?
Usually yes. Higher sheen paints may cover slightly differently. Always follow the manufacturer’s guidance.
How do I estimate primer separately?
Run the calculator once with primer coverage and your coat count for primer, then again for finish coats; add the results.
How to calculate paint for a room
- Measure length, width, and height of the room.
- Count doors and windows (we subtract standard areas automatically).
- Choose the number of coats and your paint’s coverage per gallon.
- Turn the ceiling on/off, and set a waste buffer.
- Read gallons (exact) and the suggested gallons + quarts to buy.
Paint estimating: coverage, coats, color changes, and surface prep
We built our paint estimator to keep projects on schedule and on budget. When we translate measurements into quantities with clear assumptions, it’s easier to plan labor, pick finishes, and shop confidently.
What “coverage per gallon” really means
Label coverage assumes smooth, properly primed surfaces and average application. Textured walls, fresh drywall, or drastic color shifts reduce real coverage. When in doubt, lower the coverage number or increase waste.
Coats and color changes
Deep color over light (or the reverse) often needs a high-hide primer plus two color coats. For accent walls, sample boards help confirm coverage before you buy gallons.
Openings and trim
We subtract doors and windows from wall area because they aren’t rolled like field walls. Trim, baseboards, and doors typically use a different product and sheen—estimate them separately.
Waste and touch-ups
A small buffer avoids last-minute runs when cutting in, boxing cans, or working over rough patches. Keep a labeled quart for future touch-ups; color shifts with age and light are real.