Paint Calculator
Free paint calculator. Estimate gallons and liters of paint needed from wall dimensions, coats, and coverage rate. Imperial and metric. 100% client-side.
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What is Paint Calculator?
The Paint Calculator is a free, browser-based tool that estimates how much paint your project needs. Enter the length and height of each wall, subtract doors, windows, and custom areas, then set the number of coats and the coverage rate from your paint can label. The calculator applies an adjustable waste factor, converts the result to both gallons and liters, and tells you how many whole cans to buy — with an optional cost estimate. All math runs 100% client-side — no sign-up, no data uploads.
Key Benefits
- Accurate estimates from your actual wall measurements — no more guessing at the store
- Automatic door and window deduction using standard opening sizes
- Coats, coverage rate, and waste factor all adjustable to match any paint brand
- Results in gallons and liters together so you can buy from any supplier
- Whole-can buy count rounded up so you never run short mid-project
- 100% client-side and offline-capable — your project data stays private
Common Use Cases
- •Planning an interior repaint — bedrooms, living rooms, hallways, and ceilings
- •Estimating exterior paint for siding, fences, and garden walls
- •Budgeting a painting quote with an optional cost per can
- •Comparing paint brands by coverage rate before you buy
- •Buying primer or single-coat products for rental turnovers
How to Use the Paint Calculator
- Measure your walls: Measure the length and height of each wall you plan to paint and add one row per wall. Choose Imperial (feet) or Metric (meters) to match your tape measure.
- Deduct openings: Enter the number of doors and windows to subtract standard opening sizes automatically, or add a custom excluded area for built-in closets, tiles, or trim you will not paint.
- Set paint parameters: Choose the number of coats (most walls need two), enter the coverage rate printed on your paint can (typically 350-400 ft²/gal or 8-12 m²/L), and keep the 10% waste factor for spills and touch-ups.
- Read the results: See the paintable area, total paint in gallons and liters, and the number of whole cans to buy. Optionally enter a price per can for a total cost estimate, then copy the full breakdown.
Key Features
- Unlimited walls with individual length and height for each surface
- Automatic door and window deduction using standard opening sizes
- Adjustable coats (1-4), coverage rate, and waste percentage
- Results in both gallons and liters at the same time
- Whole-can buy count rounded up so you never run short mid-project
- Optional cost per gallon or liter gives a total project cost estimate
Frequently Asked Questions
How much paint do I need for a 12x12 room?
A 12x12 ft room with 8 ft ceilings has about 384 ft² of wall (4 walls x 12 ft x 8 ft). After subtracting one door and two windows you get roughly 334 ft² of paintable area. At 400 ft² per gallon with two coats and 10% waste, you need about 1.8 gallons — buy two 1-gallon cans.
How do I calculate paint coverage per gallon?
Check the paint can label. Most interior paints cover 350-400 ft² per gallon (roughly 8-12 m² per liter) in one coat on a primed, smooth surface. Rough textures like stucco or brick can cut coverage by 20-30%, so measure conservatively or add an extra coat to your estimate.
How many coats of paint do I need?
Two coats is the standard for interior walls with a color change or over a repaired surface. One coat can work when repainting with the same color and finish. Dark colors over light walls, or light colors over dark walls, often need a primer plus two coats. The calculator supports 1-4 coats.
Why add a waste factor to a paint estimate?
Real projects lose paint to spills, roller and brush retention, cutting-in edges, and touch-ups after furniture goes back. A 10% waste factor is a safe default for smooth walls; use 15-20% for textured surfaces like stucco, brick, or popcorn ceilings.
Does one gallon of paint equal how many liters?
One US liquid gallon equals 3.785 liters. The calculator shows your result in both gallons and liters at the same time, so you can buy from US brands (sold in gallons) or local brands (sold in liters) without converting yourself.