How do I use a stud finder properly?

Calibrate it, sweep slowly in both directions, and confirm by finding both edges.

Difficulty: beginner
Time: 15 min
Read: 2 min
Safety: warning

Short answer

Calibrate it on a clear section of wall first, then sweep slowly. Find both edges of the stud and mark the centre between them — a single beep tells you an edge, not the middle.

Stud finders are frequently blamed for being unreliable when they have simply been used too fast or not calibrated. Both are easy to fix and the difference is dramatic.

Safety

A stud finder locates studs, not cables and pipes reliably. Use a multi-detector with live-cable detection as well, and stay out of the zones directly above, below and beside sockets and switches. No detector finds everything, particularly plastic pipes.

What you'll need

Stud finder or multi-detector
Pencil
Masking tape (optional)

Step by step

Read what type you have.Electronic ones sense density changes; magnetic ones find the screws or nails holding the board. Magnetic finders need no batteries and no calibration but only find fixings.
Calibrate on a clear section of wall.Most electronic finders need holding flat against the wall while switched on, away from a stud, until they signal ready. Skipping this is the main reason they give nonsense readings.
Sweep slowly and flat.Very slowly, keeping the whole base flat against the wall. Fast sweeping and tilting both produce false readings. This is the second main reason people distrust them.
Find both edges, not just one signal.Sweep left to right and mark where it triggers, then right to left and mark again. The stud centre is between the two marks. A single reading gives you an edge.
Confirm with the expected spacing.Studs are usually at regular centres — commonly 400mm or 600mm. Once you have found one, the next should be a consistent distance away. If it is not, something else is there.
Check by knocking and with a small pilot hole.Knock along the wall — solid rather than hollow over a stud. Then a fine pilot hole in an inconspicuous spot confirms it before you commit.
Use a multi-detector for cables and pipes as well.A stud finder does not reliably find live cables and finds no plastic pipes. Scan for those separately before drilling, and stay out of the zones around sockets and switches.
Watch for what confuses it.Foil-backed plasterboard, metal studs, thick or textured coatings, and pipework behind the board all produce misleading readings. If it behaves oddly, be more careful rather than less.

Tips

Mark findings on masking tape rather than the wall. It takes pencil, comes off cleanly and you can write on it.
In an older house, walls may be lath and plaster rather than plasterboard on studs. Electronic finders struggle badly with lath — the regular laths read as repeated studs.
For anything heavy, fixing into a stud is far stronger than any hollow-wall fixing. It is worth the extra few minutes to find one.

Questions people ask

Why does my stud finder give random readings?

Usually it was not calibrated on a clear section of wall, or it is being moved too fast or tilted. Both are easy to fix and transform the results.

Can a stud finder detect cables?

Only if it is a multi-detector with live-cable detection, and even then not reliably — and no detector finds plastic pipes. Use the safe zones as well.