Drywall & Plasterboard Calculator
Boarding out a room means buying the right number of sheets first time, then the finishing materials that go with them — joint compound, tape and screws. Order too few and you stop work for another trip; order too many and you are left storing full boards you cannot return.
This calculator turns each wall and ceiling into a sheet count, then works out the compound, tape and screws to finish them and rounds every material up to real purchase units — bags or buckets, rolls and boxes. Deduct doors and windows, pick a sheet size and waste allowance, add prices for a rough cost, and read a live shopping list. Everything runs in your browser.
Switch between metric and imperial at any time: metric defaults to 2400 × 1200 mm sheets with powder compound in bags; imperial to 4 × 8 ft sheets with ready-mix compound in buckets. There is no separate region selector — the default sheet size and pack sizes follow the unit switch.
How many sheets of drywall do you need?
The sheet count is area-based, not a board-by-board takeoff. For each surface the calculator works out the net area — the wall or ceiling area minus any openings — divides it by the area of one sheet, multiplies by your waste allowance, and rounds up to whole sheets. A 2400 × 1200 mm sheet covers 2.88 m²; a 4 × 8 ft sheet covers 32 ft².
Because the count comes from area, the way the boards run does not change how many you buy. Hanging sheets horizontally or vertically only changes where the joints fall, which the diagram shows, not the total. The two figures below are the same 4.0 m × 2.4 m wall boarded both ways — the board run differs, the sheet count does not.
How to use the drywall calculator
Choose metric or imperial units at the top; the calculator remembers your choice in your browser. Your unit choice also sets the default sheet size and pack sizes — sheets and the compound container switch to that system's defaults.
Open the Assumptions & materials card to pick a sheet size and thickness, set a waste allowance, and — if you want to override them — adjust the compound coverage, tape coverage, screw rates and pack sizes. Every constant the calculator uses is shown here and can be edited to match your product spec.
Add a surface for each wall and ceiling. Set the kind (wall or ceiling), enter the dimensions or a known area, and add door and window openings to walls to deduct. Each surface shows its own net area, sheets and screws; the Results panel accumulates every surface into project totals and a compound, tape and screw shopping list.
How to estimate drywall sheets and materials in 5 steps
- Choose unitsSelect metric (mm, m², kg) or imperial (in, ft², lb) at the top of the page. The default sheet size and pack sizes follow your choice.
- Pick a sheet sizeOpen Assumptions & materials and choose a sheet size and thickness — 2400 × 1200 mm and 12.5 mm by default, or 4 × 8 ft and 1/2 in in imperial — or enter a custom size.
- Add walls and ceilingsAdd a surface for each wall and ceiling. Set the kind, enter the dimensions or a known area, and add door and window openings to walls to deduct from the net area.
- Set waste and materialsChoose a waste allowance (10% or 15%, or your own) and, if needed, override the compound coverage, tape coverage, screw rates and pack sizes to match your product spec.
- Read the resultsThe Results panel shows the sheets to buy plus compound containers, tape rolls and screw boxes, each with its raw quantity — add prices for a material total and cost per area.
How much waste should you add?
Waste covers the offcuts, breakages and part-sheets you cannot avoid: the strip left after a run, a corner snapped on site, the piece cut around a window. The calculator adds it before rounding up, so it lifts the sheet count and, indirectly, the finishing materials that follow the boarded area.
Ten percent suits straightforward walls with few openings. Fifteen percent is a safer allowance for ceilings, small or awkward rooms, and jobs with lots of cut-outs, where more of each sheet ends up as offcut. Use the quick picks or type your own percentage — the override wins whenever it is a valid number.
How the compound, tape and screws are worked out
The finishing materials are derived from the same net area as the sheets, using coverage rates you can see and change, then rounded up to whole purchase units at the project level so that part-surfaces share a bag, roll or box rather than each rounding up on its own.
Joint compound is estimated by weight per area and divided by the container weight — a 25 kg bag of powder in metric, or a 61.7 lb (4.5 gallon) bucket of ready-mix in imperial. Because powder and ready-mix are a different physical basis, switching units resets the compound coverage and container to that region's defaults rather than converting a figure that would not carry across.
Every quantity is derived from the net area of each surface. Purchase units are rounded up across the whole project, so leftover coverage from one surface carries into the next.
Sheets
ceil( netArea ÷ sheetArea × (1 + waste) )- sheetArea = sheet width × sheet length (2.88 m² for 2400 × 1200 mm; 32 ft² for 4 × 8 ft).
- netArea is the gross wall or ceiling area minus any openings.
- Board orientation does not enter the count — only the diagram.
Joint compound
ceil( totalNetArea × coverage ÷ containerSize )- Default coverage 0.5 kg/m² (0.10 lb/ft²), by weight.
- Container 25 kg bag (metric) or 61.7 lb / 4.5 gal bucket (imperial).
- Coverage and container reset to region defaults when you switch units.
Joint tape
ceil( totalNetArea × coverage ÷ rollLength )- Default coverage 2.05 m/m² (0.65 ft/ft², about 20 ft per sheet).
- Roll 90 m (metric) or 500 ft (imperial).
- Paper tape by default — adjust the coverage for mesh.
Screws
ceil( totalScrews ÷ boxCount )- Wall 10.8 /m² (1.0 /ft², about 32 per 4 × 8 sheet).
- Ceiling 12.4 /m² (1.15 /ft²) — tighter spacing fights gravity.
- Box 1000-count (metric) or 1 lb, about 200 count (imperial).
Worked examples
Three quick estimates at the default coverage and pack sizes. Your own numbers will differ once you set the sheet size, waste and coverage to your spec, but these show how the sheet, compound, tape and screw quantities come together.
Worked at the default coverage and pack sizes. Materials are rounded up to whole purchase units.
Living-room wall (metric)
Wall · with a door- Given
- Wall 4.0 m × 2.4 m = 9.6 m²
- One door 0.9 m × 2.0 m = 1.8 m² → net 7.8 m²
- 2400 × 1200 mm sheets (2.88 m²), 10% waste
- Sheet formula
ceil( 7.8 ÷ 2.88 × 1.10 )- Working
- Sheets: ceil(7.8 ÷ 2.88 × 1.10) = ceil(2.98) = 3 sheets
- Compound: 7.8 × 0.5 = 3.9 kg → 1 × 25 kg bag
- Tape: 7.8 × 2.05 = 16.0 m → 1 × 90 m roll
- Screws: 7.8 × 10.8 = 84 → 1 × 1000-count box
- Result
- 3 sheets · 1 bag compound · 1 roll tape · 1 box screws
Garage wall (imperial)
Wall · no openings- Given
- Wall 12 ft × 8 ft = 96 ft², no openings
- 4 × 8 ft sheets (32 ft²), 10% waste
- Sheet formula
ceil( 96 ÷ 32 × 1.10 )- Working
- Sheets: ceil(96 ÷ 32 × 1.10) = ceil(3.3) = 4 sheets (the diagram draws 3 whole boards — waste rounds it up)
- Compound: 96 × 0.10 = 9.6 lb → 1 × 61.7 lb bucket
- Tape: 96 × 0.65 = 62 ft → 1 × 500 ft roll
- Screws: 96 × 1.0 = 96 → 1 × 1 lb box
- Result
- 4 sheets · 1 bucket mud · 1 roll tape · 1 box screws
Bedroom ceiling (metric)
Ceiling · tighter screws- Given
- Ceiling 4.0 m × 3.0 m = 12 m²
- 2400 × 1200 mm sheets (2.88 m²), 15% waste
- Sheet formula
ceil( 12 ÷ 2.88 × 1.15 )- Working
- Sheets: ceil(12 ÷ 2.88 × 1.15) = ceil(4.79) = 5 sheets
- Compound: 12 × 0.5 = 6.0 kg → 1 × 25 kg bag
- Tape: 12 × 2.05 = 24.6 m → 1 × 90 m roll
- Screws: 12 × 12.4 = 149 → 1 × 1000-count box (ceiling rate)
- Result
- 5 sheets · 1 bag compound · 1 roll tape · 1 box screws
Common mistakes to avoid
Confusing the drawn boards with the buy count. The diagram is a schematic that lays whole boards across the surface; the number to buy is higher because it includes your waste allowance and rounds up to whole sheets. Always order from the Results panel, not by counting boards in the figure.
Forgetting to deduct openings, or over-deducting. Add each door and window with its real size and count so the net area is right — but only on walls in dimension mode. In area mode the calculator treats the number you type as the finished net area and does not deduct anything.
Converting material assumptions across units. A US ready-mix coverage in gallons does not translate into a UK powder coverage in kilograms, so switching units deliberately resets the compound, tape and screw settings to the region's defaults. If you have overridden them, re-check the assumptions card after a switch.
Frequently asked questions
How many sheets of drywall do I need?
Divide the net area of each wall and ceiling by the area of one sheet, add your waste allowance, and round up. A 2400 × 1200 mm sheet covers 2.88 m² and a 4 × 8 ft sheet covers 32 ft², so a 9.6 m² wall needs about 3 sheets and a 96 ft² wall about 4 once 10% waste is added. The calculator does this for every surface and totals them.
How is the sheet count worked out?
It is area-based: sheets = ceil(netArea ÷ sheetArea × (1 + waste)). Net area is the wall or ceiling area minus any openings, sheetArea is the width times the length of one board, and waste is your chosen allowance. It is not a board-by-board cutting list, so the number is robust to how the sheets are actually laid out.
How much joint compound do I need?
Compound is estimated by weight per boarded area — about 0.5 kg/m² (0.10 lb/ft²) at the default — then divided by the container size and rounded up. In metric that is 25 kg bags of powder; in imperial, 61.7 lb (4.5 gallon) buckets of ready-mix. Coverage varies a lot by product and number of coats, so adjust it in the assumptions card to match your spec.
How much joint tape do I need?
Tape follows the boarded area at about 2.05 m/m² (0.65 ft/ft², roughly 20 ft per sheet) and is divided by the roll length — 90 m or 500 ft — and rounded up to whole rolls. The default assumes paper tape; if you use mesh, adjust the coverage in the assumptions card.
How many drywall screws do I need?
Screws are worked out per area by surface kind: about 10.8 per m² (1.0 per ft²) on walls and 12.4 per m² (1.15 per ft²) on ceilings, because ceilings need tighter spacing to hold the board against gravity. The project total is divided by the box count — 1000-count or a 1 lb box of roughly 200 — and rounded up.
How much waste should I add?
Ten percent suits straightforward walls with few openings; 15% is safer for ceilings, small rooms and jobs with lots of cut-outs, where more of each sheet ends up as offcut. Use the quick picks or type your own percentage — a valid override always wins over the preset.
Should I hang the boards horizontally or vertically?
For estimating it does not matter: the sheet count is area-based, so orientation does not change how many boards you buy. It only changes where the joints fall, which the diagram shows. Horizontal hanging is common on walls to keep seams at a comfortable taping height; vertical is often used on tall walls and where sheets meet framing cleanly.
Why do ceilings need more screws than walls?
A ceiling board is fighting gravity across its whole face, so it is fixed at a tighter screw spacing than a wall board. The calculator uses 12.4 screws per m² (1.15 per ft²) for ceilings against 10.8 per m² (1.0 per ft²) for walls, and sums both into the project screw total before rounding up to boxes.
How do I deduct doors and windows?
On a wall in dimension mode, add an opening with its width, height and count and its area is subtracted from the gross wall area before the sheets and materials are worked out. The surface row shows the net area after deductions. Openings only apply to walls; ceilings and any surface in area mode take the number you enter as the finished net area.
Does the calculator work in metric and imperial?
Both. Switch units at the top and the geometry converts — walls in m or ft, area in m² or ft², sheets in mm or inches. The material assumptions do not convert: because powder and ready-mix compound are a different physical basis, switching units resets the compound, tape and screw settings to that region's defaults rather than carrying a figure that would not translate.
Is the calculator private?
Yes. Every calculation runs entirely in your browser. Nothing you enter is sent to any server, and your project is saved only in your own browser's local storage.