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Drywall calculator

This drywall calculator is a sheet estimator that converts wall and ceiling dimensions into square footage, adds a waste factor, and returns the number of sheets to order in standard sizes — plus rule-of-thumb quantities for tape, joint compound, and screws.

Your surfaces

Enter each wall and ceiling as its own surface, and don’t subtract standard doors and windows. Measurements in decimal — 6 inches is 0.5 ft.

Covers cuts and breakage. 10% assumes standard doors and windows were not subtracted.
Pick the length that spans your walls with the fewest butt joints. 4×8 sheets are the easiest to carry.
CAD. For a materials estimate only — delivery not included.

How the math works

Drywall is estimated by area: the calculator sums each surface’s length × height, adds the waste factor you select, then divides by the coverage of one sheet — 32 sqft for a 4×8, 40 sqft for a 4×10, 48 sqft for a 4×12 — and rounds up to full sheets. Ceilings count as surfaces too: enter each one as its own length × width row.

Don’t subtract standard doors and windows. The offcuts around openings are rarely reusable, so estimating practice keeps them in the count — and the 10% waste factor assumes you haven’t subtracted them. Only deduct genuinely large openings, like a garage door or a full wall of glazing.

Choose the sheet length that spans your walls with the fewest butt joints — a 12-ft sheet on a 12-ft wall means zero. Fewer joints means less tape, less compound, and less sanding.

The finishing figures are trade rules per 1,000 sqft of board — about 370 LF of joint tape, 140 lb of ready-mixed compound, and one screw per square foot on 16-inch on-centre framing. Real usage varies with framing spacing and finish level, so treat them as ordering guides, not a takeoff.

Drywall calculator FAQ

Do I subtract doors and windows?
No. Standard estimating practice keeps openings in the count, because the offcuts around doors and windows are rarely reusable elsewhere. The 10% waste factor assumes openings were not subtracted. Only deduct genuinely large openings, like a garage door or a full wall of glazing.
What sheet size should I use?
The one that spans your walls with the fewest butt joints. A 12-ft sheet run horizontally covers a 12-ft wall in one piece per course; 4×8 sheets are easier to carry and fit through stairwells. Fewer joints means less tape, less compound, and less sanding.
How much joint compound do I need?
Roughly 140 lb (about 64 kg) of ready-mixed compound per 1,000 sqft of drywall to a standard Level 4 finish. That's a trade rule of thumb — usage rises with higher finish levels, textured finishes, and beginner technique.
How many screws per sheet?
About one screw per square foot of drywall on 16-inch on-centre framing — roughly 32 screws for a 4×8 sheet. Framing at 24-inch centres uses fewer; ceilings and code-specified assemblies can require tighter patterns. Screws are sold by the pound and by the box at GDBS.
Does this work for ceilings?
Yes. Enter each ceiling as its own surface row using length × width. Ceilings typically get the same sheet thickness or a ceiling-rated board; vaulted or angled ceilings cut with more waste, so use the 15% factor.
What about fire-rated drywall?
Fire-rated assemblies (Type X board) follow the same area math, but sheet type, thickness, and screw pattern are specified by the assembly listing — e.g. per ULC-listed designs. Calculate the sheets here, then confirm the assembly requirements before ordering.

Got your number? Sheets are heavy — local delivery runs within 100km of the Scarborough yard.

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