Paint Calculator
Calculate how much paint you need for a room.
Wall area
45.00 m²
Paint needed (L)
9.00 L
Paint needed (gal)
2.38 gal
How to use Paint Calculator
Enter Room Dimensions
Input your room's length, width, and height in feet or meters using the input fields labeled 'Length', 'Width', and 'Height'. The calculator accepts decimal values for precise measurements.
Select Paint Coverage Rate
Choose your paint type from the dropdown menu or enter the coverage rate in square feet per gallon. Standard latex paint covers 350-400 sq ft/gallon; premium paint covers 250-350 sq ft/gallon. The default value is 350 sq ft/gallon.
Specify Number of Coats
Use the 'Number of Coats' selector to choose 1, 2, or 3 coats. Most rooms require 2 coats for even coverage. Select the appropriate number using the radio buttons or dropdown.
Adjust for Windows and Doors
Toggle the 'Include Windows/Doors' checkbox and enter the number of windows and doors. Each window equals approximately 10 sq ft and each door equals 20 sq ft. The calculator automatically deducts these areas.
View Your Paint Estimate
Click the 'Calculate' button to instantly see results displayed in the 'Results' panel. View total square footage, gallons needed, and cost estimate if you entered your paint price per gallon.
Related Tools
Paint calculator: how many gallons do you need for a room?
Paint calculator: how many gallons do you need for a room?
Calculate exactly how much paint you need at ToolHQ's paint calculator, enter wall dimensions, choose your number of coats, and the calculator deducts doors and windows automatically, returning the total in gallons or liters.
A paint calculator estimates the total wall (and ceiling) area of a room, adjusts for openings, and divides by the paint's coverage rate to determine how many gallons to purchase.
Buying too little paint mid-project means a second trip and a potential color-lot mismatch. Buying too much wastes money on product you cannot return. Getting the estimate right comes down to accurate measurements and the right coverage rate for your paint type. ToolHQ's paint calculator handles both.
Key Takeaways
- Enter room length, width, and height to get wall area; add ceiling if painting it too
- Doors and windows are deducted automatically from the total wall area
- Supports both gallons (US) and liters, and any number of coats
- No data is stored or transmitted, all calculations happen locally in your browser
- Coverage rates vary by paint type, use the reference table below to pick the right one
What is a paint calculator and how does it work?
A paint calculator multiplies room dimensions to find total paintable area, subtracts door and window areas, then divides by the coverage rate of the paint to get the number of gallons needed. The core formula:
Gallons needed = (Total wall area - Openings) × Number of coats / Coverage rate per gallon
For a room 12 ft × 14 ft with 8 ft ceilings:
- Perimeter: (12+14+12+14) = 52 ft
- Wall area: 52 × 8 = 416 sq ft
- Subtract 2 doors (21 sq ft each) and 2 windows (15 sq ft each): 416 - 42 - 30 = 344 sq ft
- Two coats at 350 sq ft/gallon coverage: (344 × 2) / 350 = 1.97 gallons, round up to 2 gallons
ToolHQ's calculator does this calculation automatically. It also handles the ceiling separately (ceiling paint often has a different coverage rate than wall paint) and supports multiple rooms in a single session.
Paint quality, surface texture, and application method all affect coverage. Rough or porous surfaces absorb more paint, always add 10-15% to the estimate for textured walls, brick, or wood paneling.
All calculations run locally in your browser, no data is stored or transmitted.
When to use a paint calculator
You need a paint calculator before buying paint for any painting project:
- Repainting walls in a room before a move, renovation, or refresh
- Painting new construction where primer and two coats of color are needed
- Exterior painting where weather resistance matters and coverage rates differ
- Estimating material costs when getting quotes or comparing brands
- Planning a multi-room project where you want to order everything at once
Mini-story 1: Sandra was repainting her living room and hallway before listing her house for sale. She measured both spaces, entered the dimensions into ToolHQ's paint calculator with two doors and three windows deducted, selected two coats, and got a total of 3.4 gallons. She bought four gallons (rounding up with a buffer), painted both rooms over a weekend, and had about half a gallon left over for touch-ups later. The alternative, buying "two gallons per room" as she had done before, would have left her with surplus she could not return.
Calculate your paint needs free at ToolHQ
How to use the ToolHQ paint calculator
The process takes about two minutes:
- Go to the tool. Navigate to ToolHQ's paint calculator. No account or sign-up required.
- Enter room dimensions. Input the room length, width, and ceiling height in feet or meters.
- Add ceiling if painting it. Select the ceiling option if you are painting the ceiling, ToolHQ calculates ceiling area separately.
- Set number of doors and windows. The tool uses standard door size (21 sq ft) and window size (15 sq ft) as defaults, adjust if your openings differ.
- Choose number of coats. Most projects need two coats. One coat may suffice for a same-color refresh on a smooth surface; three coats are sometimes needed for dramatic color changes over dark paint.
- Read the result. The calculator returns gallons (or liters) needed. Always round up to the next available container size.
Paint coverage reference table
Coverage rates vary by paint type. Use this table to pick the right rate for your project:
| Paint type | Coverage per gallon | Notes |
|---|---|---|
| Standard interior latex (wall) | 350-400 sq ft | Most common wall paint |
| Flat/matte finish | 350-400 sq ft | Hides imperfections, less washable |
| Satin / eggshell | 350-400 sq ft | Balance of sheen and durability |
| Semi-gloss / gloss | 300-350 sq ft | Slightly lower coverage due to formulation |
| Interior primer | 200-300 sq ft | Seals surface before color coat |
| Ceiling paint (flat white) | 300-400 sq ft | Often one coat sufficient if repainting white |
| Exterior paint | 250-350 sq ft | Lower due to surface texture and absorption |
| Spray application | 200-300 sq ft effective | More wasteful than roller, increase estimate by 20% |
When to prime: You need primer when painting over a drastically different color (especially going lighter), over bare drywall or plaster, over stains or water damage, or on wood and metal surfaces. If your home was built before 1978, be aware that walls may contain lead-based paint, the U. S. Environmental Protection Agency provides guidance on safe handling procedures for surfaces that may contain lead paint before any sanding or stripping.
If you need to convert between gallons and liters for European paint products, ToolHQ's area converter handles unit conversions alongside your project calculations.
Mini-story 2: Marcus, a general contractor, uses ToolHQ's paint calculator for every interior paint job before sending a materials quote to clients. He enters the room dimensions, selects three coats for color changes and two for same-color refreshes, and the tool generates the quantity. He adds 10% to his order for waste and touch-ups, then multiplies by his current trade price per gallon to build the materials line item. The whole process takes under three minutes per room, replacing a spreadsheet he used to maintain manually.
Frequently asked questions
How much does one gallon of paint cover?
Standard interior latex covers 350-400 square feet per coat. Primer covers 200-300 sq ft per gallon. Always check the specific product's coverage rate on the label.
Do I need two coats or one?
Two coats are standard for most interior projects. One coat may be enough for a same-color refresh on a smooth, well-prepared surface. Going from dark to light always requires at least two coats.
Should I subtract the area of doors and windows?
Yes. Doors and windows are not painted, so subtracting them reduces the paint quantity you need. A standard door is roughly 21 sq ft and a standard window is roughly 15 sq ft.
Do I need to buy a separate paint for the ceiling?
Ceiling paint has different properties (usually flat white with higher viscosity to prevent dripping) and a slightly different coverage rate. If your ceiling needs painting, calculate it separately using 300-400 sq ft per gallon.
Is the paint calculator free?
Yes. ToolHQ's paint calculator is completely free, with no account, no sign-up, and no usage limits. All calculations happen locally in your browser.
The short version
Estimating paint quantity is straightforward when you have the right formula and coverage rate for your product type. ToolHQ's paint calculator handles wall area, ceiling area, door and window deductions, and multiple coats in one calculation, returning your total in gallons or liters. It is free, instant, and requires no account.
For other home renovation material calculations, ToolHQ's wallpaper calculator estimates rolls needed for any room, the flooring calculator handles floor materials with waste factors, and the area converter converts between square feet and square meters. Explore more calculator tools at ToolHQ.
Calculate your paint needs free at ToolHQ