Find out how much paint and how many cans you need for your walls — just enter your dimensions, doors, windows and number of coats.
Enter your wall details and click Calculate to see how much paint you need
This free paint calculator estimates how much paint and how many cans you need to cover a room's walls, based on the wall dimensions, the number of doors and windows (which reduce the paintable area), and how many coats you plan to apply. It's built for homeowners, renters, and DIY painters who want a quick, reliable estimate of gallons or liters needed before heading to the store, instead of guessing and either running short mid-project or overbuying and wasting money.
The calculator multiplies wall width by height by the number of walls to get the gross area, then subtracts a standard area for each door and window to get the net paintable area. That net area is multiplied by the number of coats and divided by your paint's coverage rate (how many square feet or square meters one gallon or liter covers) to get the total paint needed. Dividing that by your chosen can size and rounding up gives the number of cans to buy.
This paint calculator suits anyone planning a painting project who wants a numbers-based shopping list instead of a guess: first-time DIY painters tackling a bedroom or living room, experienced homeowners repainting after years of wear, landlords and property managers turning over a rental unit, and professional painters who want a fast second check before quoting a job. It works equally well in Feet/US or Meters/Metric units, so it's useful regardless of which measurement system you're used to.
Buying too little paint means an inconvenient second trip to the store — and possibly a slightly different batch or sheen, since paint tint formulas can shift between manufacturing runs. Buying too much wastes money on paint you won't use. A clear estimate of net area, total paint needed, and cans required helps you buy exactly what the job calls for, whether you're working in gallons and square feet or liters and square meters.
The exact formula this paint calculator uses to turn wall dimensions into gallons or liters
Because paint is only sold in fixed can sizes, the calculator always rounds the cans-needed figure up to the next whole can — you can't buy 2.18 gallons at the store, only whole cans that add up to at least that much.
Gross area is every wall's total surface. Net area subtracts standard door and window sizes, since you don't apply wall paint to glass or door slabs.
Coverage rate is how many square feet (or square meters) one gallon (or liter) of paint can cover for a single coat on an average, previously painted surface.
Each additional coat uses roughly the same amount of paint as the first, so paint needed scales directly with the number of coats you apply.
From measuring your walls to knowing exactly how many cans to buy
Select Feet/US or Meters/Metric depending on how you measure your walls. Switching units automatically updates the default coverage rate and can size.
Type the width and height of a typical wall, then enter the number of walls you're painting to establish the gross paintable area.
Enter how many doors and windows sit on those walls. The calculator subtracts a standard area for each to leave the net paintable area.
Enter how many coats you plan to apply and your paint's coverage rate (square feet or square meters per gallon/liter) — check the label on your paint can for the most accurate figure.
Review the net area to paint, total paint needed in gallons or liters, and the number of cans to buy, already rounded up to a whole can.
Two realistic scenarios showing exactly how the numbers are derived
A bedroom with four 12 ft × 9 ft walls, one door, two windows, two coats, and standard 350 sq ft/gallon coverage.
A 12×10 ft room with 8 ft ceilings has two walls 12 ft long and two walls 10 ft long. Since the calculator's "Wall Width" field expects one number, enter the total perimeter as the width and set walls to 1 — this gives the identical gross area as running all four walls separately. One door, one window, two coats, 350 sq ft/gallon coverage.
Explanation: Both examples reach the calculator's core formula — gross area minus door/window deductions, times coats, divided by coverage rate — from different starting inputs. Example 1 enters one wall's dimensions and a wall count; Example 2 enters a full perimeter with a wall count of 1. Either approach produces the same net area for the same physical room, which is useful when a room doesn't have four equal-length walls.
What each figure in the results panel actually tells you
| Result | What It Means |
|---|---|
| Net Area to Paint | Total wall surface after subtracting doors and windows — the actual area your paint needs to cover, per coat. |
| Paint Needed | Total volume of paint (gallons or liters) required across all coats, based on your coverage rate. |
| Cans Needed | Paint Needed divided by your chosen can size, rounded up to the next whole can — the number you'd actually purchase. |
About the 10% buffer: The figures above are the mathematical minimum for the coats and coverage you entered. They don't include a safety margin for spills, uneven application, or future touch-ups. Most painters and paint retailers recommend adding roughly 10% on top of the calculated paint-needed figure — and since cans are already rounded up to whole units, you'll often have a small natural buffer built in once you round.
If your result feels too low or too high: double-check your coverage rate against the actual paint can label (it's usually printed directly on the can or lid), and confirm you've entered coats correctly — doubling coats roughly doubles paint needed.
This calculator provides a planning estimate only. Actual paint usage can vary by brand, application method, wall condition, and color change — always round up and keep the receipt in case you need a bit more.
Where a fast, accurate paint-quantity estimate genuinely helps
Get an exact gallons-and-cans number before a weekend refresh project.
Plan paint purchases alongside other renovation materials without over-ordering.
Cross-check material estimates quickly before finalizing a client quote.
Budget paint and cans accurately between tenant turnovers.
Estimate paint quantities as part of a broader room design plan.
Estimate painting costs for a new house before move-in.
Apply the same width × height × coats formula to siding or stucco walls.
Estimate paint for larger commercial wall areas before ordering in bulk.
Plan how much base-coat paint a mural wall will need before painting begins.
Budget a fresh coat of neutral paint before listing a property for sale.
Estimate paint for large, plain wall areas common in garages and basements.
Adapt the area-based formula to estimate stain or exterior paint quantities.
Learn how area, coats, and coverage rate combine into a real-world material estimate.
What this paint calculator does well, and where it can't replace a real inspection
Reference estimates at 350 sq ft/gallon coverage and 2 coats — always confirm with your own inputs and paint label
| Room Type | Approx. Size | Ceiling Height | Net Wall Area | Paint Needed (2 coats) | 1-Gallon Cans |
|---|---|---|---|---|---|
| Small bathroom | 5 × 7 ft | 8 ft | ~171 sq ft | ~0.98 gal | 1 |
| Bedroom | 10 × 12 ft | 8 ft | ~316 sq ft | ~1.81 gal | 2 |
| Bedroom (larger) | 12 × 14 ft | 9 ft | ~432 sq ft | ~2.47 gal | 3 |
| Living room | 15 × 18 ft | 9 ft | ~543 sq ft | ~3.10 gal | 4 |
| Garage / basement | 20 × 20 ft | 10 ft | ~764 sq ft | ~4.37 gal | 5 |
These figures assume one standard door and one or two standard windows deducted per room, smooth previously-painted drywall, and 350 sq ft/gallon coverage. Enter your room's exact dimensions, openings, coverage rate, and coats into the calculator above for a precise figure.
Summary: This paint calculator turns your wall dimensions, door/window count, coats, and coverage rate into a clear gallons-or-liters figure and a ready-to-buy can count — a fast, free planning step before any painting project. Pair it with related tools like the Wallpaper Calculator and Tile / Flooring Calculator for a fuller home-project material plan.
Common questions about estimating paint and cans
Official guidance to complement this calculator — not a substitute for a professional painter's assessment
Other home & project tools