How to estimate paint for a room
Measure correctly, apply a realistic coverage rate, and add a small buffer.
TL;DR
- Area × coats ÷ coverage = paint needed (then round up).
- Coverage on the can is a starting point—texture and color changes reduce it.
- Add a small buffer for touch-ups and waste (often 5–10%).
A good paint estimate comes down to two numbers: surface area to paint and coverage per gallon (or per liter). Add the number of coats, then include a small buffer for touch-ups and waste.
If you measure once and calculate once, you usually under-buy. This guide explains what to measure and why the coverage number on the can is only a starting point.
Step-by-step: paint math
- Measure wall area (length × height) for each wall and sum them.
- Subtract large openings (doors, big windows) if you want a tighter estimate.
- Decide coats (often 2 for new colors or big color changes).
- Pick a realistic coverage rate based on wall texture and paint type.
- Add 5–10% buffer, then round up to whole cans.
Practical tips
- Textured walls and deep colors reduce coverage.
- Ceilings and trim often use different paint and finish.
- Primer can reduce coats, but it is not “free paint”.
- Batch-mix cans (boxing) for consistent color across walls.
Common mistakes
- Forgetting to multiply by coats (2 coats is common).
- Using ideal label coverage for rough or porous surfaces.
- Skipping a buffer and running short mid-project.
Want the fast estimate?
Use our paint calculator and share a link that keeps your inputs.
FAQ
Should I subtract windows and doors?
For small openings, the difference is usually within your buffer. Subtracting is useful for very large windows, many doors, or tight budgets.
Why is my result higher than the can label coverage?
Label coverage assumes ideal conditions. Texture, porosity, application method, and multiple coats all reduce real-world coverage.
How much extra paint should I buy?
A 5–10% buffer is common. If you need exact color matching later, buying an extra can from the same batch can save time.
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Browse all guides →Last updated: Dec 2025
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