How do I cut plasterboard accurately?

Score and snap for straight cuts, the pad saw for openings, and cutting to fit an uneven wall.

Difficulty: beginner
Time: 30 min
Read: 3 min
Safety: caution

Short answer

Score the paper face with a sharp knife against a straightedge, snap the board over an edge, then cut the back paper. For sockets and openings, measure from two fixed points and cut with a pad saw from the face side.

Plasterboard is cut by breaking it rather than sawing it, which is faster, cleaner and far more accurate once you trust it.

Safety

Plasterboard sheets are heavy and awkward — get help lifting full sheets rather than risking a back injury. Gypsum dust irritates eyes and airways, so wear eye protection and a mask when sanding or cutting with power tools. Check for cables and pipes before cutting into an existing wall.

What you'll need

A sharp utility knife with spare blades
A long straightedge or a plasterboard T-square
A pad saw or jab saw for openings

Step by step

Mark and score the face paper.One firm pass with a sharp knife against a straightedge. You are cutting the paper, not the gypsum — pressing harder does not help.
Snap it over an edge.Stand the board on edge, knee behind the score, and push. The core breaks cleanly along the line.
Cut the back paper.Fold it open and run the knife down the crease. The offcut falls away with a clean edge.
Tidy the edge with a rasp.A plasterboard rasp or a surform takes off the ragged core so the board sits tight against its neighbour.
Measure openings from two fixed points.For a socket, measure from the floor and from the nearest board edge to both sides of the box. Transferring one measurement is how holes end up 20mm out.
Cut openings from the face side.A pad saw plunged through, cutting on the pull stroke. Cutting from the back tears the face paper you will be skimming.
Cut slightly generous on internal cuts.A socket cut that is 2mm large disappears behind the faceplate. One that is 2mm tight means recutting the board.
Scribe to an uneven wall.Hold the board in position, run a pencil against the wall with a small block, and cut to that line. Rooms are rarely square.
Leave a small gap at the floor.10 to 15mm, so the board is not wicking moisture and can be lifted tight to the ceiling. It is covered by skirting.

Tips

Change the knife blade often. A blunt blade tears rather than scores and the snap goes off line.
Cut socket openings from the face side so the face paper stays intact.
Leave a gap at the floor — the skirting covers it and the board stays out of any damp.

Common mistakes

Trying to saw a straight cut — It is slower, dustier and less accurate than score and snap, and it tears the paper faces which then need more filling.
Transferring a single measurement for a socket cut — Any small error compounds and the hole misses the box. Measure from two fixed references to both edges of the opening.

If it doesn't work

Snap went off the line

Cause: Blunt blade or an incomplete score — Fix: One firm continuous pass with a fresh blade against a straightedge.

Socket hole in the wrong place

Cause: Measurement transferred from one reference — Fix: Patch the hole with an offcut and filler, and measure from two points next time.

Board will not sit flat

Cause: Ragged cut edge — Fix: Rasp the edge back to the line.

Gap at an uneven wall

Cause: Board cut square to a wall that is not — Fix: Scribe the board to the wall profile before cutting.

Questions people ask

Do I need a special knife?

No, a sharp utility knife is standard. What matters is changing the blade often — a dull blade is the main cause of a snap that wanders off the line.

Which side do I score?

The face side, which is the one you will skim or decorate. Score, snap away from the score, then cut the back paper.

How do I cut a curve?

Score the face repeatedly along the curve, or use a pad saw. For tight curves, score the back paper in strips and bend the board around a former.