Drywall Calculator
How much drywall do you need? Measure any number of rooms, add a waste factor, and get the square footage, quantity and cost to order.
A worked example
A 12 × 15 ft room is 180 square feet. Adding the 10% waste factor this calculator defaults to brings that up to 198 square feet to buy — 7 sheets, at 32 sq ft each. At the mid-range price of $2.50 per square foot that is about $495.00.
| Grade | Price per sq ft | 180 sq ft room, installed |
|---|---|---|
| Budget | $1.50 | $297.00 |
| Mid-range | $2.50 | $495.00 |
| Premium | $3.50 | $693.00 |
Price ranges are broad US ballpark figures for material plus typical installation, gathered as placeholders and not yet verified against sourced pricing. Use them to sanity-check a quote, not to replace one. A standard 4×8 ft drywall sheet covers exactly 32 sq ft. 4×12 ft sheets cover 48 sq ft.
To compare quotes on the same basis, see how to calculate price per square foot.
Counting sheets, not square feet
Drywall is estimated by area and bought by the sheet. A 4 × 8 ft sheet covers 32 square feet, a 4 × 12 covers 48. Add up the wall area — each wall’s width times the ceiling height — plus the ceiling if you are boarding it, then divide and round up.
A 12 × 15 ft room with an 8 ft ceiling has 432 square feet of wall plus 180 of ceiling: 612 square feet, which is 20 sheets of 4 × 8 once you allow for cuts. Add a couple of spare sheets on any job over a few rooms; a board damaged in handling is common and a second trip is not free.
Openings usually stay in the total
Unlike flooring, drywall estimates normally count a wall as solid and treat door and window openings as waste. The cut-out from a standard opening is rarely large or square enough to use elsewhere, so deducting it leaves you short. Deduct only where the openings are genuinely large — a wall of glass, or a wide cased opening between two rooms.
Sheet size, compound and tape
Longer sheets mean fewer butt joints, which are the hardest joints to finish invisibly, so 4 × 12 gives a better result on any wall over 12 feet long. They are also heavier and awkward around a stairwell or a tight corner, which is why 4 × 8 hung horizontally remains the practical choice for most rooms.
For finishing, allow roughly one gallon of ready-mixed joint compound and about 40 linear feet of tape per 100 square feet of drywall for a standard three-coat finish. A level 5 finish, which skim-coats the whole surface, roughly doubles the compound. Buy tape generously — it is cheap, and running out mid-wall costs an afternoon.
Frequently asked questions
How do I calculate how much drywall I need?
Measure the wall and ceiling area in square feet, then divide by the coverage of a sheet and round up. A 4 by 8 ft sheet covers 32 square feet, a 4 by 12 ft sheet covers 48. A 12 by 15 ft room with an 8 ft ceiling has 432 square feet of wall plus 180 of ceiling — 612 square feet, or 20 sheets of 4 by 8 with the usual allowance.
Should I subtract doors and windows from a drywall estimate?
Not usually. The cut-out from a door or window opening is rarely large enough to use anywhere else, so most estimators count the wall as solid and treat the openings as part of the waste. Deduct only where the openings are large — a full wall of glass, or a wide opening between two rooms.
How much joint compound and tape do I need?
As a working figure, allow about one gallon of ready-mixed compound and roughly 40 linear feet of tape per 100 square feet of drywall for a standard three-coat finish. A level 5 finish, which skim-coats the whole surface, roughly doubles the compound. Buy tape generously: it is cheap and running out mid-wall costs an afternoon.
Should I use 4x8 or 4x12 sheets?
Longer sheets mean fewer butt joints, which are the hardest joints to finish invisibly, so 4 by 12 gives a better result on a wall over 12 ft long. They are also heavier and harder to carry up a stairwell or around a tight corner. For most rooms, 4 by 8 hung horizontally is the practical compromise.