Thickness is the easiest dimension to mis-copy when a job mixes metric drawings, imperial stock lists, and gauge callouts. Converting carefully keeps weight estimates from drifting. The SheetMetalCalc calculator accepts manual thickness in millimeters or inches and can resolve gauge only in the context of a selected material. This guide focuses on conversion discipline, not on replacing certified supplier data.

Millimeters and inches

The calculator uses standard conversions internally:

• 1 inch = 25.4 mm
• 1 mm = 0.0393700787 in (display rounded)

Enter thickness in mm or in directly in manual mode. Length and width may use additional units (cm, m, ft) but thickness inputs are limited to mm and in, matching shop practice for sheet gauge.

Converting a decimal inch to mm

Example: 0.075 in stock list on a metric drawing

0.075 × 25.4 = 1.905 mm

Enter 1.905 mm or 0.075 in in manual mode. Results should match either way after normalization.

Gauge is not a universal thickness unit

A gauge integer maps through a material-specific table. Converting “14 gauge” to mm requires knowing whether the part is mild steel, stainless, aluminum, copper, or brass. Steps:

1. Select the material in the calculator.
2. Switch to gauge mode and pick the number.
3. Read the resolved mm thickness in the results summary or reference table.

Do not copy mm from a steel chart onto an aluminum job. See Sheet Metal Gauge Chart.

When to bypass gauge entirely

• Supplier provides certified decimal thickness.
• You measured with a caliper.
• The gauge on the print conflicts with your vendor’s chart.
• The material has no gauge table in the calculator (always use manual thickness in that case).

Worked comparison (same blank, different thickness sources)

Blank 1000 mm × 1000 mm mild steel, quantity 1:

• Manual 2 mm: mass ≈ 7.85 kg at 7850 kg/m³
• Gauge 14 (table-resolved ≈ 1.897 mm): a different thickness yields a different mass. Run both in the tool rather than mentally substituting.

Length/width vs thickness units

It is fine to type length in feet and thickness in mm. The engine converts each dimension independently. Avoid converting thickness to length units by accident (for example, entering 2 m thinking it is 2 mm).

Related articles

• How to Calculate Sheet Metal Weight
• Sheet Metal Weight Calculation Guide
• Steel vs Aluminum vs Stainless

FAQ

Can I enter thickness in cm?

Not in the current UI: only mm and in for thickness. Convert cm to mm (×10) first.

Does the calculator convert gauge to inches for me?

It stores both mm and in per gauge row; calculations use mm → meters.

What if my gauge is between listed rows?

Use manual thickness from measurement or supplier data.