Metal buying guides / Materials
Sheet Metal Gauge vs. Thickness: Steel and Aluminum
A gauge number needs the material beside it. The same gauge can represent a different thickness in steel and aluminum. For a cut-to-size request, include the actual thickness in inches or millimeters whenever you can.
Updated
Quick answer
A gauge number is not a universal thickness. In the reference chart below, 16-gauge standard steel is 0.0598 inch and 16-gauge aluminum is about 0.0508 inch. Specify the material and actual thickness together.
This matters when replacing a panel, comparing listings, or transferring a dimension from an old drawing. A matching gauge number alone does not settle the match.
A short gauge comparison
These are nominal chart values, not measured thickness guarantees. The Metal Supermarkets gauge chart lists the underlying values by material.
On a small screen, scroll the table sideways to see every column.
| Gauge | Standard steel, inches | Aluminum, inches |
|---|---|---|
| 14 | 0.0747 | 0.0641 |
| 16 | 0.0598 | 0.0508 |
| 18 | 0.0478 | 0.0403 |
| 20 | 0.0359 | 0.0320 |
Use the appropriate chart for stainless or galvanized steel; don't silently carry the standard-steel column across. The chart is a translation aid. Your order still needs a material specification and a required thickness.
What that difference means on a replacement panel
Suppose an old drawing says “16 ga steel,” and a replacement listing says “16 ga aluminum.” Using the chart above, the aluminum is approximately 0.0090 inch thinner: 0.0598 − 0.0508 = 0.0090. That is about 0.23 millimeter, or 15% of the steel chart thickness.
This calculation only compares thickness. It does not compare stiffness, strength or suitability. It does show why matching the gauge number can miss the dimension you meant to preserve. If a channel, clip or spacer controls the fit, record its dimensions before choosing the replacement.
Fractions and decimals describe thickness directly
Some common inch equivalents are useful when reading a tape, drawing, or product page:
On a small screen, scroll the table sideways to see every column.
| Fractional inch | Decimal inch | Millimeters |
|---|---|---|
| 1/8 | 0.125 | 3.175 |
| 3/16 | 0.1875 | 4.7625 |
| 1/4 | 0.250 | 6.350 |
| 3/8 | 0.375 | 9.525 |
| 1/2 | 0.500 | 12.700 |
The conversion uses 25.4 millimeters per inch. Writing an exact conversion doesn't make two commercially sold nominal sizes interchangeable. For example, 3 millimeters is not exactly 1/8 inch. Check whether the difference is acceptable for the job.
What to do with an old part
Record the material information you have, the measured thickness, and where you measured it. Wear, corrosion, coatings, or a bent edge can complicate the reading. If possible, compare several sound locations and identify whether the surface coating is included.
Keep “measured” and “specified” separate in your notes. A reading from an old part is useful evidence, but it doesn't prove the original nominal thickness or alloy.
For an unknown specification, submit the measurements and explain that the original material is unresolved. Don't choose the nearest gauge simply to fill the form.
Thickness and cut tolerance are different
Cutting a plate to width and length does not set the stock thickness. If the piece must fit into a narrow slot or finish to a particular thickness, include that requirement. It may call for different stock or additional processing.
See cut-metal tolerances and fit for a worked example of allowable variation.
Rapid Metals' standard materials are described by grade and inch dimensions. If your drawing calls for another thickness, request that specific material instead of selecting a close size and hoping it fits.