Home Calculators Drill Bit Size

Drill Bit Size Calculator

Select your screw/bolt size and material to find the correct drill bit diameter — plus the pilot hole and clearance hole sizes.

Select Your Requirements

Fastener Type

Size

Material Being Drilled

Pilot Hole (Thread)

—

Select options to calculate

Clearance Hole

—

For bolt to pass through

Countersink

—

For flush screw head

Bolt Size	Pilot Hole	Clearance Hole	Thread Pitch	Spanner Size
M3	2.5mm	3.2mm	0.5mm	5.5mm
M4	3.3mm	4.3mm	0.7mm	7mm
M5	4.2mm	5.3mm	0.8mm	8mm
M6	5.0mm	6.4mm	1.0mm	10mm
M8	6.8mm	8.4mm	1.25mm	13mm
M10	8.5mm	10.5mm	1.5mm	17mm
M12	10.2mm	13.0mm	1.75mm	19mm
M16	14.0mm	17.0mm	2.0mm	24mm
M20	17.5mm	21.0mm	2.5mm	30mm
M24	21.0mm	25.0mm	3.0mm	36mm

Wood Drilling Tips

Use a sharp HSS or brad-point bit. Drill at medium speed. Clamp your workpiece to prevent splintering.

Metal Drilling Tips

Use a cobalt or titanium-coated HSS bit. Drill slowly with cutting fluid. Centre-punch the mark first.

Masonry Drilling Tips

Always use a carbide-tipped masonry bit with a hammer drill. Match drill size to rawl plug size exactly.