What this tool works out
This tool matches a drill bit type to the material you are drilling and reports the size for the wall plug you are using.
The bit size is straightforward — it matches the plug. The bit type and the drill setting are where most damaged bits, cracked tiles and oversized holes come from.
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Before you drill
- Check for cables and pipes with a detector before every hole. Cables commonly run vertically and horizontally from sockets and switches, and detectors are not infallible.
- The bit size should match the plug, not the screw. A 7 mm plug needs a 7 mm hole.
- Identify the material first. Plasterboard sounds hollow; a magnet or detector will find the studs behind it.
- Wear eye protection. Dust and fragments come back towards you, particularly when drilling overhead.
Hammer action shatters brick and block, which is exactly what you want in masonry and exactly what you must avoid in tile, plasterboard or wood. Drilling tile on hammer will crack it, usually as the bit breaks through. Switch it off, get through the glaze and body, then switch it on for the masonry behind if needed.
How this calculator works
A lookup by material, with the plug size carried through:
Brick or block → masonry bit, hammer mode
Wood → wood or brad-point bit, no hammer
Metal → HSS bit, low speed and steady pressure
Tile → tile or glass bit, no hammer until through the tileDepth matters as much as diameter. Drill slightly deeper than the plug so dust in the bottom of the hole does not stop the plug seating — a strip of tape on the bit is the usual way to mark it.
Where the fixing manufacturer specifies a hole size or depth, that specification takes precedence over any general guidance.
Worked example: a 7 mm plug in brick
Using the default figures — brick or block with a 7 mm plug:
- Suggested bit: 7 mm masonry bit, hammer mode
Two details the tool does not state. Modern high-density blocks and engineering brick can be hard enough that a standard masonry bit struggles — an SDS drill makes a substantial difference. And aerated blocks, the light grey kind, are soft enough that a standard plug pulls straight out; they need plugs designed for aerated concrete, which is worth knowing before hanging anything on them.
Common mistakes
- Drilling tile on hammer mode. It cracks, usually just as you break through.
- Sizing the bit to the screw. It matches the plug.
- Not drilling deep enough. Dust in the bottom stops the plug seating fully.
- Drilling near a socket or switch without checking. Cables run in predictable zones and hitting one is dangerous.
- Using an ordinary plug in aerated block. It will pull out under load.
Frequently asked questions
How do I know what my wall is made of?
Tap it — plasterboard sounds hollow and drums, masonry sounds solid. Drill a small test hole somewhere hidden and look at the dust: grey or red dust means masonry, white powder means plasterboard, and grey powder that stops quickly then goes hollow means dot and dab plasterboard on masonry. Wood shavings mean you have found a stud.
Where do cables run in walls?
Safe zones under the wiring regulations are within 150 mm of the top of a wall, within 150 mm of a corner, and in a vertical or horizontal band aligned with any socket or switch. Cables should be in those zones, but older wiring frequently is not. Use a detector, and treat the area around any accessory as suspect.
What size hole for a screw with no plug?
In wood, drill a pilot hole roughly the diameter of the screw's core, excluding the thread — for a 4 mm screw that is around 2.5 mm. Hardwood needs a clearance hole in the top piece as well, so the screw pulls the two together rather than jacking them apart.
Do I need an SDS drill?
For occasional holes in ordinary brick, no — a decent combi drill copes. For engineering brick, dense concrete blocks or anything more than a few holes, an SDS drill is transformative and can be hired cheaply for a day. They are also considerably less tiring.
Is what I select stored?
No. Your selections are processed in your browser and never transmitted or retained.
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References
- Health and Safety Executive — power tool safety, dust control and avoiding buried services
- GOV.UK — Approved Document P and rules on electrical work in dwellings
Sources are checked at publication and can change — how I choose and check references.