Order paint once, not twice

Running out mid-room means a colour match risk and a wasted trip. Ordering far too much ties up cash. A paint calculator turns room size into litres so you can buy with a clear number, then still leave a little for touch-ups.

This tool is for Canadian renos and painting crews on a phone. Coverage is entered in square metres per litre, which matches most Canadian can labels. You also see US gallons if a supplier still talks that way.

How the paint calculator works

Wall area is the room perimeter times wall height: 2 × (length + width) × height. Standard door and window openings are subtracted so you are not painting glass. Multiply by the number of coats, add your waste percent for cutting-in and texture, then divide by coverage (m² per litre) from the product data sheet.

Default coverage of 10 m² per litre is a starting point for smooth interior walls. Dark colours, porous drywall, and heavy texture drink more paint — lower the coverage number or raise waste.

Ceilings, trim, and exterior

This version estimates wall paint for a rectangular room. For ceilings, treat length × width as a single surface (use a square room with height 0 is not supported — use length × width as a separate mental calc or set a square footprint with low height carefully). For trim and doors, many painters buy by the quart or litre for cutting-in rather than full wall math.

Exterior masonry and rough siding often need more product per square metre. Always check the manufacturer coverage for the product and surface.

Print, share, or save

Print or Share PDF gives the client or helper a one-page estimate. Signed-in users can save a frozen sheet to TradeInvoice Docs or a job. Pair the paint sheet with a quote when you price labour and materials.

Frequently asked questions

Is the paint calculator free?

Yes. Calculate, print, and share without an account. Saving to Docs needs a free TradeInvoice account.

Should I use metric or imperial?

Use metres when plans and cans use metric. Use feet when the room was measured that way. Coverage stays in m² per litre — convert if your can only lists sq ft per gallon (about 400 sq ft/gal ≈ 9.8 m²/L).

How many coats should I use?

Two coats is common over a similar colour. Primer plus two finish coats is safer on new drywall or large colour changes.

What waste percent should I use?

Five to ten percent covers cutting-in and small touch-ups. Use more for textured walls, many colours, or roller loss on exterior.