Measuring Wire and Electrode Diameter

What it is

Filler metal is sold by diameter as well as classification. North American stock is labeled in fractional or decimal inches; imported and global stock is labeled in millimeters. The two systems are close but not equal, and mixing them causes feed problems, wrong contact tips and wrong drive rolls. AWS A5.18 lists standard wire sizes in both units and sets diameter tolerances.

How to measure

1. Use a micrometer or digital caliper. Zero it first.
2. MIG wire: cut a clean end, straighten a short length, and measure in two directions at right angles.
3. Stick electrode: measure the bare core wire at the grip end. Never measure over the coating.
4. TIG rod and tungsten: measure the bare rod away from any flag or label.
5. Compare to the chart. The reading should sit very close to one size.

Size chart

Key points

• .030 in is about 0.76 mm and .045 in is about 1.14 mm. They are close to 0.8 and 1.2 mm, not exact.
• Drive rolls, liners and contact tips must match the wire size actually on the spool.
• Flux-cored wire can be slightly out of round. Measure in two directions and average.
• Stick electrode size is the core wire. A 1/8 in rod will measure much larger over the coating.
• Package labels show the nominal size. Trust the label first and measure only when it is missing or in doubt.

Common mistakes

• Measuring stick rods over the flux.
• Loading 0.8 mm wire into a .035 setup.
• Using a ruler instead of a caliper.
• Assuming a metric spool equals the inch size printed on the old box.

Governing standards: AWS A5.18; AWS A5.1; AWS A5.12 (tungsten).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.