How many metres of wire are on a spool
A spool is sold by mass while the feeder counts metres per minute. This converter ties the two together: how much wire is really on there, how many minutes of arc it is, and how far the weld will run.
Where the length comes from
Wire is a cylinder, so the mass per metre is the cross-section times the
density: g/m = π·d²/4 · ρ. With the diameter in millimetres the
area in mm² is numerically the volume in cm³ per metre, so the formula reduces
to a multiplication. Length is the spool mass divided by the mass per
metre.
| Wire Ø, mm | g/m | m in 5 kg | m in 15 kg |
|---|---|---|---|
| 0.6 | 2.2 | 2250 | 6750 |
| 0.8 | 3.9 | 1270 | 3800 |
| 1.0 | 6.2 | 810 | 2430 |
| 1.2 | 8.9 | 563 | 1690 |
| 1.6 | 15.8 | 316 | 950 |
At the same diameter an aluminium spool holds nearly three times the metres a steel one does: density 2.70 against 7.85 g/cm³. That is why a 2 kg aluminium spool lasts longer than it looks — though the feed speed on aluminium is noticeably higher too.
Why bother working it out
- Ordering for a job. Metres of weld times consumption per metre gives kilograms, and those give the number of spools to have on the shelf.
- Planning a shift. At 8 m/min a 15 kg spool of 1.0 mm wire is about 300 minutes of pure arc — roughly two shifts on a wire feeder.
- Judging what is left. Weigh the part-used spool with its hub, subtract the empty mass, and you know at once whether you will finish the joint.
Frequently asked questions
Why is there less wire than the calculation says?
The last turns at the hub never come off — the feed loses the arc before it reaches the end. Spools also come in light within tolerance. Treat the figure as an upper bound and knock a few per cent off for the remainder.
Does it work for flux-cored wire?
Not directly. Flux-cored wire has a core of a different density from the sheath, so its mass per metre comes out lower than solid wire of the same diameter — usually by 10–20 %. For an exact figure take the mass per metre from the maker’s data sheet.
Where do I get the consumption per metre of weld?
From the deposited metal calculator: it gives the kilograms of consumable per metre for a particular preparation. Put that number in here and you get how far one spool goes.
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