How to measure caster wheels.
Replacement casters fail on measurement more than on quality. Six measurements, taken with a tape and calipers in five minutes, decide whether the new caster fits, matches and carries like the old one.
Measure: (1) wheel diameter across the tread; (2) wheel width across the tread — the dimension that also decides the US tariff heading; (3) overall height from floor to the top of the mounting; (4) for plates: plate size and bolt hole spacing in both axes; (5) for stems: diameter, length and thread pitch or grip-ring type; (6) swivel radius if clearance is tight. Photograph the caster next to the tape for each measurement.
1–2. Diameter and width — and why width is the professional's measurement
Diameter is measured across the tread at its widest point, including the tyre. Width is measured across the tread face. Width is the measurement amateurs skip and professionals start with, for two reasons. It decides how the load spreads and how the wheel behaves. And for US importers it decides the tariff classification: under HTS Chapter 83 Note 2, a caster only sits in heading 8302.20 if its diameter is 75 mm or less, or its wheel width is under 30 mm. A replacement programme that changes width by a few millimetres can change the heading of every shipment — our tariff guide covers the rule in full.
3. Overall height — the fit dimension
Overall height (floor to mounting surface, caster standing as installed) decides whether the equipment sits level and whether all four casters touch the ground. When replacing one caster of a set, match overall height exactly; when replacing a set, confirm the new height against the equipment's clearance — oven doors, conveyor interfaces and dock levellers all care.
4. Plate pattern
Measure the plate's overall length and width, then the bolt hole spacing centre-to-centre in both axes, and the bolt diameter the holes accept. Record all five numbers. 'Standard plate' is not a measurement, and the caster industry runs several standards that differ by millimetres.
5. Stem dimensions
For threaded stems: outside thread diameter, usable length, and pitch (use a thread gauge, or count threads over 10 mm and divide). For grip ring stems: stem diameter, length, and the ring position; better, identify the socket standard or send a sample. State whether dimensions are metric or inch — near-miss cross-standard fits are a classic source of loose casters.
6. Swivel radius and offset
If the caster swings near a frame member, guard or another caster, measure the swivel radius — centre of the mounting to the wheel's furthest swing point. Replacement forks with different offsets change this radius and the equipment's steering feel.
Sending measurements to us
The RFQ form takes a photo or specification link for a reason: a photograph of each measurement, tape in frame, settles in seconds what paragraphs of email debate. Add the load case and the floor, and a replacement quotation can be locked against your measurements — or send a sample, and we will measure it for the record and keep the dimensions against your reorders.
Related guides
Specification first. Price second.
Every guide on this site ends at the same place: a locked specification and a sample that proves it.