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Drywall Calculator

Sheets for a room, plus the joint compound, tape and screws that people end up going back for.

Enter the room size, or the wall area if you already have it.

Waste and price

Ten percent is the usual minimum.

Estimate. A real-world figure based on the assumptions listed below, which you can change.

How this calculator works

Wall area is the perimeter times the ceiling height — for a 12 by 10 room with 8-foot ceilings that is 44 feet of perimeter and 352 square feet of wall. The ceiling adds another 120 if you are boarding it.

Doors and windows are subtracted, but the offcuts around them are usually unusable, so the waste allowance is doing double duty there. On a room with ordinary openings the two roughly cancel; on a wall that is mostly patio door they do not, and the page says so rather than quietly under-ordering.

Sheets are the easy part, and they are not what sends people back to the store. Joint compound, tape and screws follow from the board actually hung rather than from the room, and the usual figures are about 4.5 gallons of compound and 370 feet of tape per 1,000 square feet, with roughly 32 screws to a 4×8 sheet at 16-inch framing centres.

Those figures are manufacturer estimating guidance rather than a standard. They move with the finish level you are working to, how far apart the framing is, and how tidy the hanging was — so they are shown as estimates and the assumptions are stated.

The formula

Exactly what happens to your numbers, step by step.

  1. Area

    walls   = 2 × (length + width) × ceiling height
ceiling = length × width

  2. Sheets

    sheets = ⌈(area − openings) × (1 + waste) ÷ sheet area⌉

    A 4×8 sheet is 32 ft², a 4×12 is 48 ft².

  3. Finishing materials

    compound ≈ 4.5 gal per 1,000 ft²
tape     ≈ 370 ft per 1,000 ft²
screws   ≈ 32 per 4×8 sheet

A worked example

A 12 ft by 10 ft room with 8 ft ceilings, one door and one window, walls only.

What you enter

Room
12 ft × 10 ft × 8 ft
Openings
1 door, 1 window
Sheet size
4 ft × 8 ft
Waste
10%

The working

Wall area
2 × (12 + 10) × 8 = 352 ft²
Less openings
352 − 32 = 320 ft²
With 10% waste
352 ft²
Sheets
352 ÷ 32 = 11
Compound and tape
~1.6 gallons, ~130 ft

11 sheets, about 1.6 gallons of compound and 130 feet of tape

Note that the waste allowance almost exactly replaces the openings you subtracted. That is not a coincidence — it is why rough estimates that ignore both often land close, and why a room with unusually large windows needs a second look rather than the default.

Assumptions

Every result here rests on these. Change your inputs and the result changes with them.

  • Walls are boarded floor to ceiling with no allowance for a partial height.
  • A doorway is about 3 ft by 6 ft 9 in and a window about 3 ft by 4 ft.
  • Framing is at 16-inch centres, which sets the screw count.
  • The finishing figures are manufacturer estimating guidance for a standard finish.

What this cannot tell you

  • Openings are counted by number at a standard size, not measured. A patio door or a picture window is far larger, and on a wall like that you should enter the area directly instead.
  • It does not plan the sheet layout. A real hanger orients sheets to minimise joints, and an awkward room can need an extra sheet that no area calculation predicts.
  • Corner bead, adhesive, primer and the fasteners for a ceiling are not estimated.
  • Finishing quantities vary a great deal with the level of finish. A Level 5 skim uses considerably more compound than the Level 4 these figures assume.
  • It assumes a rectangular room with a flat ceiling. Vaulted ceilings, soffits and stairwells all need measuring separately.

Questions people ask

How many sheets of drywall do I need?

Divide the wall area by the sheet area and round up, after subtracting openings and adding waste. A 12 by 10 room with 8-foot ceilings needs about 11 sheets of 4×8 for the walls alone.

Should I use 4×8 or 4×12 sheets?

Longer sheets mean fewer joints to tape and a flatter finished wall, which is why professionals prefer them. They are also heavy and awkward — a 4×12 half-inch sheet is around 80 pounds and genuinely hard to handle alone in a tight space.

How much joint compound will I need?

Roughly 4.5 gallons per 1,000 square feet of board for a standard finish. A skim-coated Level 5 finish uses substantially more, and a garage that only needs taping uses less.

How many screws per sheet?

About 32 for a 4×8 sheet on walls at 16-inch framing centres. Ceilings need more because gravity is working against you, and 24-inch centres need fewer per sheet but hold less well.

Do I subtract doors and windows?

This does, and then the waste allowance covers the offcuts around them, which are mostly unusable. For ordinary openings the two roughly cancel out. For a wall that is mostly glass, enter the actual area instead — the standard-size assumption will be well off.

Related calculators

Sources and review

Sources

  • Manufacturer estimating figures: ~4.5 gallons of compound and ~370 ft of tape per 1,000 ft²; ~32 screws per 4×8 sheet at 16-inch centres

Methodology version 1.0.0 · Last reviewed