How to measure a room for a quote: gross and net wall area, openings and skirting

Most quoting mistakes start before anyone opens a spreadsheet: a wall measured from the wrong corner, a window that never got written down, a skirting run that includes the doorway. The quote looks fine, then the job eats the margin.

Here's how to measure a room so the figures hold up, whatever you use to write the quote.

Start with the shape

For a rectangular room you need two figures: length and width. Measure wall to wall. If the room is old, take each figure at both ends. Walls are rarely square in a Victorian terrace, and a 50 mm difference across a floor is worth knowing about before you order anything.

An L-shaped or odd-shaped room is easier if you go round it wall by wall. Start in one corner and measure the first wall. Note whether you turn left or right at the next corner, and keep going until you're back where you started. That gives you two checks for free:

• The walls running one way should add up to the same as the walls running back (2.8 m out means 2.8 m back).
• If the outline doesn't close, one reading is wrong. Better to find out while you're still standing in the room.

Then measure the ceiling height. In older houses, check it in more than one place. If the ceiling slopes or is vaulted, a single height won't describe it. Write a note and take photos so whoever prices the job knows.

Floor, ceiling and perimeter

With the shape and the height, you can work out the basics:

• Floor area is length × width for a rectangle. For an L-shape, split it into two rectangles and add them, or take the big rectangle and subtract the missing corner.
• Ceiling area is the same as the floor area when the ceiling is flat.
• Perimeter is the total length of all the walls. Flooring fitters need it for gripper rods and beading, and decorators need it for skirting.

Gross and net wall area

Gross wall area is the perimeter × the ceiling height: every wall, as if there were no doors or windows.

Net wall area is the gross figure with the doors, windows and other openings taken off. It's what you'll actually paint, plaster, paper or tile.

Which one you price on is a business decision. Some decorators price materials on net and labour on gross, because cutting in around a window takes longer than painting the same area of plain wall. Whatever you choose, use the same rule every time and say on the quote which one you used. Then the customer can't argue the figure is wrong, and you can compare one job with the next.

Why openings matter

Every door, window and opening changes three things: the net wall area, the skirting length and the work itself.

For each one, write down:

• Width and height. A standard internal door in England and Wales is 1981 mm high and 762 mm wide (6'6" × 2'6"). Widths of 686 mm and 838 mm are common too, so measure rather than assume.
• How many. A wall of matching windows is quicker to write as one line with a count.
• What happens to it. Is it staying, being replaced, being removed or going in new? A new doorway means making good and an extra architrave. A replaced window can mean new reveals and a new sill. These are the things that turn up as extras later if nobody wrote them down.

Watch out for doors between two rooms. Record them in both rooms so each room's figures are right, but only count the door once when you add up the doors for the whole job.

Skirting length

Skirting is the perimeter less the doorways. Skirting doesn't run across a door opening, so take each doorway's width off.

A few things catch people out:

• Kitchens. Skirting usually stops where the base units start, so take the unit run off too.
• Radiators. Skirting usually runs behind them, so leave the radiator in.
• Bay windows and chimney breasts. They add wall length. Measure every face rather than the straight line across.

A worked example

A bedroom, 4.0 m × 3.2 m, with a 2.4 m ceiling, one standard internal door (0.762 m × 1.981 m) and one window (1.2 m × 1.2 m):

Leave the openings out and you'd price nearly 3 m² of wall that isn't there. Forget to take off the doorway and you'd order skirting for a gap.

Fixtures and extras

The room shape doesn't tell you everything. While you're there, count the fixtures and note what happens to each one: radiators and towel rails, WCs, basins, baths, showers, light points and switches. Then add the measurements the shape doesn't give you, like a worktop run, tiling to 1.2 m or a splashback.

Take photos of every wall, not just the interesting one. A photo answers questions nobody thought to ask on site.

Doing it on your phone

All of this works with a tape, a pencil and the back of a job sheet. The trouble starts when that sheet has to get back to the office, or when someone rings the engineer for the bathroom sizes again.

Field Forge Room surveys do it in the field app. The engineer picks the room type and enters the shape: length and width, or wall by wall with left and right turns. The app shows how close the outline comes to closing. They add the ceiling height, doors, windows, fixtures, extra measurements, notes and up to 30 photos a room. Floor area, gross and net wall area, ceiling area, skirting length and perimeter are worked out as they type. If they used a laser, they can mark the figure as laser-measured. It all works with no signal and sends when signal comes back.

Within moments of the engineer measuring, the office sees every room on the job, on the quote it was taken for and on the customer's site. Room surveys come with every Field Forge plan.

Start your free 30-day trial, no card needed