How to estimate plasterboard: sheets, screws and stopping compound

Running out of plasterboard halfway through a job costs you a trip to the merchant and half a day. This guide shows how to estimate plasterboard (drywall in the US and Canada): how many sheets, how many screws, how much stopping compound (called mud or joint compound in the US) and how much tape. Metric comes first, with US units in brackets.

Step 1: measure the walls and ceilings

Work room by room. Write each number down as you go.

• Walls: add up the length of every wall in the room, then multiply by the stud height. That gives the wall area in square metres (square feet).
• Ceilings: multiply the room length by the room width.
• Openings: take off large openings like doors, windows and wardrobe gaps. Many estimators leave small openings in, because the offcut is usually wasted anyway.
• Extras: add bulkheads, window reveals, stair stringers and boxed-in pipes. These are small, but they add up.

Step 2: pick your sheet sizes

Plasterboard comes in different lengths. A common sheet in New Zealand and Australia is 2400 by 1200 mm, which is 2.88 square metres. In the US and Canada, the standard sheet is 4 by 8 feet, which is 32 square feet. Longer sheets are also made, such as 2700, 3000 and 3600 mm (9, 10 and 12 feet).

• Longer sheets mean fewer end joints, which means less stopping and fewer cracks
• Match the sheet length to the stud height or room length where you can
• Don’t order sheets longer than your crew can safely carry and lift, or than you can get into the house

Step 3: work out the number of sheets

Here is the simple method:

1. Add up the total area for walls and ceilings.
2. Add a waste allowance. Use about 10 percent for simple, square rooms. Use about 15 percent for rooms with lots of openings, angles or bulkheads.
3. Divide by the area of one sheet.
4. Round up to the next whole sheet.

For a more accurate count, sketch each wall and draw the sheets on it. This also shows you where the joints will land, which matters for a good finish. See how to hang plasterboard for layout tips.

Remember that wet areas, fire-rated walls and bracing walls may need special boards. Count those separately.

Step 4: screws, compound and tape

These are rough planning figures for ordering. Your plasterboard system’s fixing pattern and the product data sheets set the real numbers.

• Screws: many estimators allow about 32 to 40 screws per standard sheet. Ceilings and bracing walls often need more.
• Stopping compound: a common rule is about 0.4 litres of ready-mixed compound per square metre of board for all coats (about 1 US gallon per 100 square feet). Allow more for a higher level of finish. Powder compounds have their own coverage on the bag.
• Tape: tape length equals the total length of all the joints. A rough guide is 2.5 to 3.3 metres of tape per square metre of board (750 to 1,000 feet per 1,000 square feet).
• Corner beads: measure every outside corner and window reveal edge, then round up to whole lengths.
• Adhesive: if your system uses it, check the coverage on the tube or bag.

A worked example

You are lining a bedroom that is 4 metres by 3.5 metres, with a 2.4 metre stud. There is one door and one window.

• Wall length: 4 plus 3.5 plus 4 plus 3.5 equals 15 metres
• Wall area: 15 times 2.4 equals 36 square metres
• Take off the door (about 1.6 square metres) and the window (about 1.2 square metres): 33.2 square metres
• Ceiling: 4 times 3.5 equals 14 square metres
• Total: 47.2 square metres (about 508 square feet)
• Add 10 percent waste: about 52 square metres
• Divide by 2.88: just over 18, so order 19 sheets of 2400 by 1200

In US units, 508 square feet plus 10 percent is about 559 square feet. Divided by 32, that is about 17.5, so order 18 sheets of 4 by 8.

For the extras, allow about 700 screws, about 19 litres of ready-mixed compound (about 5 US gallons) and roughly 120 to 150 metres of tape (400 to 500 feet).

Common mistakes

• Forgetting the ceiling, or measuring it as if it were a wall
• No waste allowance, then running one sheet short on the last wall
• Ordering standard board for a wet area or fire wall
• Using lots of short sheets to save money, which adds joints and stopping time
• Not counting bulkheads, reveals and boxing

Pricing the job

Once you know the quantities, you can price materials and labour. Many plasterers price hanging and stopping per square metre (per square foot), or per sheet. Check your price against your own records. The job costing guide shows how to track what jobs really cost, and gib stopping basics explains the coats you will be pricing.

If you are planning a whole house, the free House Planner shows ceiling areas for the plan you draw.

Quick checklist

• Measure every wall and ceiling, room by room
• Take off large openings, keep small ones in
• Add 10 to 15 percent waste
• Divide by the sheet area and round up
• Count wet-area, fire and bracing boards separately
• Order screws, compound, tape and corner beads to match
• Check the manufacturer’s fixing pattern and data sheets