What it is called, by market
One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.
United Kingdom
Same word, different thinggauge
also batten gauge, SWG, screw gauge, gauge rod, gauging
BATTEN GAUGE is a roofing distance in millimetres. GAUGING is mixing plaster. SWG is a legacy wire scale differing from the American one. Four unrelated senses before leaving a single site.
Australia
Same word, different thinggauge
also B&S gauge, batten gauge, sheet gauge
Metric thicknesses in millimetres are now standard for sheet, with gauge surviving in speech and in imported product data — so a gauge number on an Australian job is usually somebody else's scale.
United Statesyours
Same word, different thinggauge
also AWG, sheet metal gauge, wire gauge, ga
AWG for wire and a SEPARATE sheet metal gauge for steel, and they are different scales: 16 AWG wire and 16 gauge steel have no dimensional relationship at all.
Canada
Same word, different thinggauge
also AWG, sheet gauge, mil
As the United States, with MIL a further trap — a thousandth of an inch in North American usage, and a millimetre in casual speech elsewhere.
The governing standard, by market
United Kingdom
BS 3737 legacy / BS EN 10143
Historic standard wire gauge, and continuously hot-dip coated steel sheet thickness tolerances, which are specified in millimetres.
United States
ASTM B258 / ASTM A480
Standard nominal diameters for solid round wires (AWG), and general requirements for flat-rolled stainless and heat-resisting steel, which use decimal inches.
Calculators for this
Each works in either measurement system, and the terminology on the page follows whichever market you have selected.
Frequently asked questions
- Why does a bigger gauge number mean thinner material?
- Because the scale counts drawing operations, not dimensions. Wire was made by pulling it through successively smaller dies, and the gauge number recorded how many times it had been drawn — so more passes meant a thinner wire and a higher number. Sheet gauge has a related history in the number of rolling reductions. The scale is therefore inverted relative to every other dimension on a drawing, and it is not linear either: the step between 10 and 12 is a different physical amount from the step between 20 and 22. That is why a gauge number cannot be scaled, interpolated or converted arithmetically — it has to be looked up in the right table, and the right table depends on the material and the market.
- Is 16 gauge wire the same thickness as 16 gauge sheet?
- No, and they are not even close. AWG 16 wire is about 1.29 mm in diameter; 16 gauge steel sheet is about 1.52 mm thick, and 16 gauge for a non-ferrous sheet is a different figure again because sheet gauge tables are material-specific. There is no relationship between the two scales beyond the coincidence of using numbers. The practical consequence on a mixed job is that gauge is not a unit and cannot be carried between trades: an electrician's 16 and a sheet-metal worker's 16 describe unrelated dimensions. That is also the reason European and Australian practice moved to stating millimetres directly, and why any specification crossing markets is safer quoting the thickness.
- What does gauge mean on a roof?
- A distance, and this is the sense with no relation to any of the others. The batten gauge is the spacing from one tile or slate batten to the next, measured centre to centre, and it equals the covering's length minus the required headlap, divided by the number of courses covering a given tile. It is quoted in millimetres or inches like any other dimension, it rises and falls with the roof pitch because the lap does, and it is what a roofer sets out with a gauge rod. Nothing about it is inverted and nothing about it is a lookup table. The same word in the same conversation may mean the thickness of the flashing lead, the gauge of the fixing nail, and the spacing of the battens — three unrelated quantities.