Paint Cost Estimator

Calculate paint quantities and total project cost for rooms, walls & ceilings. Add deductions for doors and windows, include sundries, and download a PDF estimate — everything runs in your browser, nothing is uploaded.

Paint Specifications

Standard latex paint covers 350–400 sq ft per gallon. Darker colours or bare drywall typically need an extra coat.

Rooms & Surfaces

Add each room. For each room, add surfaces (walls, ceiling, accent wall). Enter width × height in feet. Doors and windows are deducted automatically.

Sundries & Supplies

Check any items to include in the total estimate.

Project Summary

Cost Breakdown

Surface Net Area (sq ft) Cans Cost

How it works

This estimator calculates the net paintable area for each surface, then divides by coverage to get cans, rounding up to whole cans every time.

Net wall area (Width × Height) − (doors × 20 sq ft) − (windows × 15 sq ft)
Ceiling area Width × Depth of room (enter depth as "width", height as "length")
Paint needed (cans) ⌈ Net area × coats ÷ coverage per can ⌉ (always round up)
Paint cost Cans needed × price per can

Example: A 12 ft × 9 ft wall with 1 door and 1 window has a net area of (12 × 9) − 20 − 15 = 73 sq ft. With 2 coats and 400 sq ft/can: ⌈73 × 2 ÷ 400⌉ = 1 can.

Frequently asked questions

How much paint do I need for a 12×12 room with 9 ft ceilings?
A 12×12 room with 9 ft ceilings has four walls totalling 12+12+12+12 = 48 linear feet × 9 ft = 432 sq ft gross. Subtract a typical door (20 sq ft) and two windows (30 sq ft total) = 382 sq ft net. With 2 coats and 400 sq ft/can: ⌈382 × 2 ÷ 400⌉ = 2 cans for walls. The ceiling adds 12 × 12 = 144 sq ft net, requiring 1 more can. Total ≈ 3 gallons of paint. Use this calculator to account for your exact dimensions.
Why do I always round up the number of cans?
Paint is sold in whole cans — you cannot buy 0.3 of a gallon at a hardware store. Rounding down would leave you short mid-project. This estimator uses ceiling division (⌈x⌉) so you always have enough. Leftover paint can be stored sealed for touch-ups, which is good practice anyway.
What are the standard door and window deduction sizes?
A standard interior door is roughly 3 ft × 6 ft 8 in = 20 sq ft. A standard window is roughly 3 ft × 5 ft = 15 sq ft. These are commonly used industry estimates. If your doors or windows are significantly larger (e.g. French doors, picture windows), enter a custom deduction by adjusting the count — or note that adding 0.5 of an "extra door" effectively deducts an additional 10 sq ft.
Should I add a waste factor for painting?
Many professionals add 10–15% extra to account for roller waste, texture absorption on older walls, and colour variation between batches. The coverage per can field lets you enter a reduced figure (e.g. 340 sq ft instead of 400 sq ft) to bake in this buffer automatically. Textured or porous surfaces like brick or bare drywall may need even more — reduce coverage to 250–300 sq ft per gallon for those.
Does this estimator include primer?
Primer is listed as an optional sundry item in the Supplies section. If you are painting over a dramatically different colour, new drywall, or raw wood, adding one coat of primer significantly improves coverage and colour accuracy, and is nearly always worth the cost. Primer is typically cheaper than finish paint and covers 300–400 sq ft per gallon as well.
Is my project data sent to a server?
No. All calculations happen entirely in your browser using JavaScript. The PDF is also generated client-side using pdf-lib. Nothing you enter is transmitted to any server, logged, or stored anywhere outside your own browser tab. You can even disconnect from the internet after the page loads and the tool will continue to work.