21 gauge steel thickness calculator
In the Manufacturers Standard Gauge for steel, 21 gauge is 0.0329 in (0.836 mm). The gauge number counts down as the sheet gets thicker.
Where the neutral axis sits, as a fraction of thickness. 0.33 for tight bends, 0.5 for generous ones.
- Thickness in inches
- 0.032 90
- Weight of the sheet
- 13.120
- Weight per square metre
- 6.560 kg/m2
- Weight per square foot
- 0.6094 kg/ft2
- Minimum inside bend radius One thickness is a safe general rule for mild steel; check the alloy.
- 0.836
- Bend allowance
- 1.864
- Bend deduction
- 1.479
- Suggested V-die opening Eight times thickness is the usual air-bending starting point.
- 6.69
Show the working
- Sheet length = 2000
- Sheet width = 1000
- Steel density = 7850
- Bend angle = 90
- K-factor = 0.42
- Thickness = 0.83566 = 0.835 66
- Thickness in inches = 0.835 66 / 25.4 = 0.0329
- area_m2 = 2000 * 1000 / 1e6 = 2
- volume_m3 = 2 * 0.835 66 / 1000 = 0.001 671 32
- Weight of the sheet = 0.001 671 32 * 7850 = 13.1199
- Weight per square metre = 0.835 66 / 1000 * 7850 = 6.559 93
- Weight per square foot = 6.559 93 * 0.09290304 = 0.609 438
- Minimum inside bend radius = 0.835 66 * 1 = 0.835 66
- Bend allowance = rad(90) * (0.835 66 + 0.42 * 0.835 66) = 1.863 97
- Bend deduction = 2 * (0.835 66 + 0.835 66) * tan(rad(90)/2) - 1.863 97 = 1.478 67
- Suggested V-die opening = 0.835 66 * 8 = 6.685 28
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- weight = length x width x thickness x density
- bend allowance = angle in radians x (inside radius + K x thickness)
- bend deduction = 2 x (inside radius + thickness) x tan(angle/2) - bend allowance
Gauge numbers are not a single standard. Steel, aluminium, stainless and zinc all use different gauge tables for the same number, so always state the material.
The Manufacturers Standard Gauge descends from a weight-per-square-foot table, which is why the thicknesses are not a neat progression.
Frequently asked
How thick is 21 gauge steel?
0.0329 inches, or 0.836 mm, for uncoated sheet steel.
Is a higher gauge number thicker?
No. The gauge number counts down as thickness goes up, so 16 gauge is thicker than 20 gauge.
Where the numbers come from
- Thicknesses are the Manufacturers Standard Gauge for uncoated hot- and cold-rolled sheet steel.