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Derrick
Derrick

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How China's company registration code uses ISO 7064 check digits (and why it matters for importers)

#opensource #data #webdev

If you've ever sourced products from China, you've probably seen an 18-character code on your supplier's business licence. It looks something like this:

91440300MA5FJK2W30

This is the Unified Social Credit Identifier (USCI) — China's equivalent of a company registration number. And buried in its last character is a check digit based on ISO 7064 Mod 31-3.

What the code tells you

The 18 characters encode specific information:

  • Position 1: Registration authority type
  • Position 2: Organization category
  • Positions 3-9: Regional code (maps to province/city/district)
  • Positions 10-17: Organization identifier
  • Position 18: Check digit (ISO 7064 Mod 31-3)

The check digit math

The validation uses a weighted sum mod 31, with weights cycling through powers of 3. Here's a JavaScript implementation:

function validateUSCI(code) {
  const CHARS = '0123456789ABCDEFGHJKLMNPQRTUWXY';
  const WEIGHTS = [1,3,9,27,19,26,16,17,20,29,25,13,8,24,10,30,28];

  let sum = 0;
  for (let i = 0; i < 17; i++) {
    sum += CHARS.indexOf(code[i]) * WEIGHTS[i];
  }
  const remainder = sum % 31;
  const expected = remainder === 0 ? '0' : CHARS[31 - remainder];
  return expected === code[17];
}
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Note: USCI uses a custom character set — no I, O, S, V, Z (to avoid visual confusion with 1, 0, 5, U, 2).

How well does it work?

I ran an exhaustive test: for every position in every sample code, I substituted every possible character and checked whether the check digit caught the error.

Result: 100% detection of single-character substitutions across 2.9 million simulated errors.

For comparison, the US VIN (Vehicle Identification Number) check digit only catches 92.5% of single-character errors.

The full dataset is on Zenodo: https://zenodo.org/records/15589531

Why this matters

If a supplier sends you a business licence with a typo in the registration code — or a completely fabricated code — the check digit catches it instantly, before you spend time on a manual lookup.

Some other findings from our research:

  • 42.5% of NHTSA-registered Chinese manufacturers can't be found by English name alone in China's registry
  • 25.4% of China's "little giant" manufacturers don't have import/export in their registered business scope
  • 53.4% of those manufacturers have changed their company name at least once

I built a free tool that does this validation plus a manual cross-reference against official Chinese registry data:

https://currawongweb.com/verify/

The research papers and datasets are all open access. Happy to answer questions about the methodology.

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