What Is CN Size in Shoes? The Definitive Conversion Guide

Navigating international shoe sizing is a guaranteed way to lose confidence at checkout. When a size chart suddenly reads “CN 40” or “CN 250,” your standard US or EU benchmarks no longer apply.

Unlike Western sizing systems which rely on arbitrary numbers, Chinese (CN) shoe sizing is highly literal—it is grounded strictly in the exact length of your foot. However, relying on generic, conflicting conversion charts across different websites often leads to incorrect fits and inevitable returns.

Whether you are trying to figure out what a CN 40 shoe size equates to, or you are staring at a mysterious “250” label on a shoebox, this guide cuts through the noise. We will break down exactly what CN means in shoe size, how it correlates to your foot length in millimeters, and how to convert it flawlessly to your local fit.

The TL;DR: CN shoe sizing is fundamentally based on foot length in millimeters. For example, a “CN 250” means the shoe fits a foot measuring exactly 250mm (25cm). As a quick benchmark, a CN 40 generally translates to a US Women’s 9 or US Men’s 7.5.

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What Does “CN” Mean in Shoe Sizes? The Two Systems

In footwear, “CN” simply stands for China. The official Chinese sizing standard is an adaptation of the international Mondopoint system—a framework designed to prioritize exact physical measurements over arbitrary numbering.

However, shopping becomes confusing because manufacturers frequently alternate between two entirely different formatting systems on their labels. Here is exactly how to decipher them:

• Format 1: The Official Millimeter Standard (The 3-Digit Code)
  This is the modern, accurate, and straightforward system. A three-digit number explicitly states the foot length in millimeters that the shoe is built for. If you see a label reading CN 240, it means the shoe is engineered for a foot measuring exactly 240 mm.
• Format 2: The Commercial Euro-Style Standard (The 2-Digit Code)
  For commercial ease, many brands still use a two-digit format that mimics European sizing (e.g., CN 39). While a CN 39 is often treated as equivalent to an EU 39, exercise caution: Chinese lasts (the physical molds used to shape the shoe) generally run slightly narrower and feature a lower instep than their European counterparts.

Editor’s Tip: When a retailer provides both formats, always rely on the 3-digit millimeter measurement. It is a literal physical dimension that leaves zero room for translation errors.

Foot Length in Millimeters: The Key to Perfect CN Sizing

Because the modern CN system is literal, knowing your exact foot measurement in millimeters unlocks your true size immediately. There is no guessing game. To get an accurate reading, avoid estimating based on your current sneakers and follow this precise method:

The Golden Rule of CN Sizing: Always round UP to the next 5-millimeter increment. Do not round down or to the nearest. For example, if your foot measures exactly 242 mm, you have outgrown the 240 mm last, so your correct choice is CN 245. If you measure 247 mm, you must step up to CN 250. This ensures your toes have the bare minimum clearance required for a comfortable stride.

The Master Conversion Matrix: CN to US, EU, and UK

Before consulting the chart below, completely disregard any advice that tells you to add arbitrary millimeters to your foot measurement. If your bare foot measures 250 mm, your true baseline is CN 250 (Format 1) or CN 40 (Format 2).

Instead of manipulating the math, adjust for your foot’s volume using this simple sizing strategy:

• For narrow or standard feet: Stick exactly to the chart’s recommendation based on your bare foot measurement.
• For wide feet, high insteps, or thick socks: Do not artificially add length to your measurement. Instead, locate your true size on the chart and simply move up one full size bracket (e.g., step up from a CN 40 to a CN 41).

Foot Length (mm)	CN Size (EU Style)	US Women’s	US Men’s	UK	EU
230 mm	CN 36	6	4.5	3.5	36
235 mm	CN 37	6.5	5	4	37
240 mm	CN 38	7.5	6	5	38
245 mm	CN 39	8	6.5	5.5	39
250 mm	CN 40	9	7.5	6.5	40
255 mm	CN 41	9.5	8	7	41
260 mm	CN 42	10	8.5	7.5	42
265 mm	CN 43	10.5	9	8	43
270 mm	CN 44	11	10	9	44
275 mm	CN 45	12	10.5	9.5	45

🔍 Quick Conversions at a Glance

For shoppers looking for instant answers on the most common crossover sizes:

What is a CN 40 Shoe Size?
A CN 40 is engineered for a foot length of precisely 250 mm (25.0 cm). In standard US sizing, this seamlessly translates to a Women’s 9 or a Men’s 7.5.

What is a CN 42 Shoe Size?
A CN 42 is engineered for a foot length of precisely 260 mm (26.0 cm). In standard US sizing, this translates to a Women’s 10 or a Men’s 8.5.

The Buyer’s Playbook: How to Avoid Fit Disasters

Do CN shoe sizes run small? The short answer is yes. But the structural reality is that they run narrow.

Footwear manufactured primarily for the Asian market is built on lasts (shoe molds) that feature a lower instep and a significantly slimmer width profile than standard US or European footwear. If you have wide feet, high arches, or suffer from bunions, ordering your exact length equivalent will almost certainly result in a shoe that pinches. In these cases, moving one full size up is non-negotiable.

⚠️ The Major Red Flag to Watch For

Never purchase from a retailer or product page that only lists a two-digit size (e.g., “CN 40”) without providing the corresponding millimeter measurement (e.g., “250mm”).

A “naked” CN 40 is often a lazy, non-standardized estimate from the manufacturer, attempting to quickly map an Asian size to Western buyers. Without the millimeter anchor, you are gambling on the fit. Always demand the foot length chart.

The Foolproof Seller Message Template

When purchasing expensive or highly structured footwear (like boots or formal heels), eliminate the guesswork entirely. Copy and paste this exact template when messaging customer service before checkout:

“Hello, my exact bare foot measurement is [X] mm long and [Y] mm wide at the widest point. Based on the specific last and instep height of this model, which CN size do you guarantee will fit?”

Frequently Asked Questions (FAQ)

Do Chinese (CN) shoe sizes typically run small compared to US sizes?

Yes, but strictly in width and volume, not in length. While the physical length of a CN shoe is mathematically exact, Chinese footwear is predominantly constructed on narrower lasts with much lower insteps than Western shoes. If you have a standard or wide American/European foot, the shoe will likely feel restrictive. If you have a wide foot or high arch, sizing up is highly recommended.

What does the decimal number in brackets mean on a CN shoe tag, like CN 250 (2.5)?

The primary number (250) dictates the exact foot length in millimeters. The decimal number in parentheses (e.g., 2.5) is an older Chinese girth/width indicator. Historically, this scale ran from 1 (narrowest) to 5 (widest) to indicate foot volume. However, in modern international e-commerce, this metric is largely obsolete and frequently inaccurate. You can safely ignore the bracketed number and focus entirely on the millimeter length.

What if my bare foot measures exactly between two CN sizes?

Never round down. If your bare foot measurement lands completely between two standard intervals—for example, measuring exactly 247 mm (between CN 245 and CN 250)—always default to the next 5-millimeter increment up. In this case, you would purchase the CN 250. This fractional allowance accounts for natural foot swelling throughout the day and provides necessary sock clearance without ruining the structural fit of the shoe.

The Final Verdict

Decoding the Chinese shoe sizing system is not about memorizing complex conversion charts; it is about trusting the physics of your foot. By abandoning the confusing two-digit approximations and anchoring your choice to the literal millimeter measurement, you eliminate the guesswork entirely.

Measure precisely, acknowledge your foot’s width, and round up when necessary. Once you master the CN millimeter rule, your days of gambling at checkout and dealing with frustrating international returns are officially over.