What Leather Ounces Mean

Leather ounces describe thickness. They don't tell you how heavy the hide feels in your hands. That's the first thing to get straight, because the label looks like a weight and trips up plenty of beginners.

What the number points to

In leathercraft, an ounce is a measurement of thickness¹. One ounce is about 1/64 inch, or about 0.4 mm¹. So a piece sold as 4 oz is about 1/16 inch thick, or about 1.6 mm¹.

An Australian leather supplier puts it the same way. It says the unit does not convey weight in the formal sense, but rather the thickness².

Each extra ounce adds another small step. Think of it as a ruler with very fine marks, where the marks happen to be called ounces.

Why it's called a weight

Here's where it gets muddy. One supplier says leather thickness is usually represented as a weight in ounces, and that the number should reflect the weight of one square foot of leather³. Another says plainly that an ounce is a measurement of thickness¹.

Both ideas sit behind the same label. In practice you'll use the number to judge thickness. When you need a figure you can measure, convert it to millimetres.

If the seller's chart shows a thickness next to the ounces, go by the thickness. It's the part you can check with a gauge.

Where you'll see which unit

Leather thickness is often measured in ounces in the US and millimetres in most other countries¹. Another supplier says it is typically measured in ounces in the USA². So if you shop from both sides of the world, you'll see the same leather described two ways. That's normal.

The ASTM test method for measuring leather says thickness may be reported in millimetres, ounces, or irons⁴. The third unit is covered on the irons page.

A label with a range

A hide listed as 3-4 oz isn't promising one exact number. The Australian supplier's chart gives 3-4 oz as 1.2 to 1.6 mm, and it notes that each piece of leather has a slightly variable thickness over the entire hide². The range is there to cover that spread.

For more on how thickness varies, see why thickness varies across a hide.

Reading a label in practice

• Find the ounce figure or range.
• Remember it's a thickness, so a higher number means a thicker piece.
• Look for a millimetre or inch figure beside it. If there isn't one, convert it yourself.
• Measure a sample if your project is fussy about thickness, using a gauge or caliper.

That's all the number does. It's a thickness label wearing a weight's name.

Some sellers print only the weight and say nothing more. Ask them whether the figure is a thickness or a weight per square foot. Their answer decides how you read the rest of the label.