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What Size Screw Is This? A Fast Measurement Checklist

Use this quick checklist to determine unknown screw size by diameter, length, head, and thread details before buying replacements.

Measure The Correct Length

For countersunk screws, measure full length from tip to top of head. For non-countersunk heads, measure from tip to underside of the head.

Length errors are common and cause seating issues even when thread size is correct.

Use the widest outer thread crest as major diameter. Mixing up core diameter vs major diameter leads to wrong size labels.

Capture multiple photos if threads are worn or damaged.

A measured diameter can map to several standards. Pair it with pitch (metric) or TPI (imperial) to lock in a true match.

If your equipment mix is unclear, compare both candidate standards before ordering.

Wood, sheet metal, and machine screws are not interchangeable by size alone. Validate tip style and thread form for your target material.

Choosing by dimensions only can still fail under load or strip mating threads.

For countersunk heads yes, for non-countersunk heads no. Measure to the underside for pan/round/hex heads.

Yes. Different pitch or thread standards can share close diameters but still be incompatible.

Confirm four fields before purchase: head type, diameter, pitch/TPI, and length measurement method.

Use Screw Identifier to capture a photo, add ruler reference, and verify thread specs in seconds.