Knife & Pan Size Converter (inches ⇄ cm)

Understanding the knife and pan size converter — concept and principle

Kitchen tools are sold in inches in some markets and in centimetres or millimetres in others. A chef's knife may be listed as 8 in in a US shop and as 20 cm or 210 mm in a Japanese or Korean one, and a frying pan may be called 11 in or 28 cm. This converter turns any knife length or pan diameter from inches to centimetres or back, and also shows millimetres, so you can compare listings, replace a lid or check that a pan fits your burner or oven.

How it is calculated

• Inches to centimetres: cm = in × 2.54.
• Centimetres to inches: in = cm ÷ 2.54.
• Millimetres: mm = cm × 10.

Results are rounded to 0.1 cm (0.01 in in the table) and to whole millimetres. Knife lengths refer to the blade only, from the heel (where the blade meets the handle) to the tip. Pan sizes are normally the inside diameter across the top rim.

The principle

Since the international yard and pound agreement of 1959, the inch has been defined as exactly 25.4 mm. Because the factor is exact, the conversion has no error of its own; any difference you see between two listings comes from rounding by the maker or from measuring a different part of the tool. Japanese makers usually round knife blades to a neat millimetre figure, which is why an 8 in (203 mm) chef's knife is often compared with a 210 mm gyuto, and a 10 in knife with a 240 mm one. Pans follow the same idea: a 28 cm pan is 11.0 in, so it is sold as an 11 in pan in the US.

Worked example

1. Default input: I have inches, size 8.
2. Centimetres: 8 × 2.54 = 20.32 cm, rounded to 20.3 cm.
3. Millimetres: 20.32 × 10 = 203.2 mm, rounded to 203 mm.
4. Back to inches: 20.32 ÷ 2.54 = 8 in, confirming the round trip.

How to read the result

Treat the result as the nominal size, not a precise measurement. For knives, a difference of 5 to 10 mm between two brands that both say 8 in is normal. For pans, the top diameter is larger than the flat cooking base, often by 3 to 5 cm on a flared frying pan, so check the base size when matching a pan to an induction zone. A lid labelled with the same diameter as the pan should fit, but measure the rim if the brands differ.

Common mistakes

• Measuring a knife including the handle, which can add 10 to 13 cm.
• Comparing a pan's top diameter with another pan's base diameter.
• Using 2.5 instead of 2.54, which makes a 12 in pan 30 cm instead of 30.5 cm.

Frequently asked questions

What is a 10-inch chef's knife in cm?

10 × 2.54 = 25.4 cm, or 254 mm. It is usually compared with a 240 mm or 250 mm Japanese blade.

What size is a 24 cm pan in inches?

24 ÷ 2.54 = 9.45 in, so it is commonly sold as a 9.5 in pan.

Is a 20 cm pot the same as an 8-inch pot?

Almost. 8 in is 20.32 cm, a difference of about 3 mm, which most lids tolerate.

Sources: BIPM, The International System of Units (SI Brochure), 9th edition, 2019 · NIST Special Publication 811 (2008), Guide for the Use of the International System of Units, Appendix B