Americans usually meet the sort code the way most people meet a foreign plug socket: when something that works perfectly well at home refuses to fit. A sort code is the UK's institution identifier, the field that does the job a routing number does in the United States, and the differences between them are small but consequential when you are the one filling in the form.
Same job, different shape
A sort code is six digits and identifies a UK institution, and historically a clearing point inside it. A routing number is nine digits and identifies a US institution, with the first two digits encoding a Federal Reserve district and the ninth digit acting as a checksum over the other eight. Both are routing fields: they say where, not who. Neither is valid in the other country's system, and a payment form that asks for one will reject the other outright rather than misroute it, which is at least a small mercy.
The check digit difference matters
A US routing number can be arithmetically tested on its own. Multiply the digits by a fixed weighting and the total is divisible by ten if the number is well formed, which is why a mistyped routing number is usually caught at the point of entry. A UK sort code carries no such property. Six digits that are the wrong six digits are simply a different, possibly live, sort code. UK systems compensate by putting the check on the account number instead, and by running a name check when a payee is set up.
What a US payer actually needs to send money to the UK
For a payment from a US bank to a UK account you will generally not use the sort code directly. You will need the recipient's IBAN, which already contains the sort code and account number inside it, and the recipient bank's BIC, which is the international institution identifier. Several UK banks publish exactly this guidance for their own customers to pass on. If the form you are on asks for a sort code as well, giving it does no harm, but the IBAN is what routes the payment.
Where the sort code still shows up for you
If you hold a UK account, for example for a UK employer, a UK landlord or a UK subsidiary, the sort code is the field you will be asked for every time a domestic payment is set up. It will appear with your account number on statements and in the app's account details screen. It is not confidential in the way a card number is, because UK pull payments require a mandate, but it is worth treating with the same care as any detail that directs where money goes.
Questions people ask about what is a bank sort code
Is a sort code the same as a routing number?
They do the same job in their own countries. A sort code is six digits for the UK, a routing number is nine digits for the US, and neither works in the other system.
Can I send money to a UK account with just a sort code?
Not from abroad. An international payment normally needs the IBAN and the BIC. The sort code and account number are the domestic UK pair.
Does a sort code have a check digit?
No. Unlike a US routing number it carries no checksum, which is why UK systems put the arithmetic check on the account number instead.
Why is my UK sort code written with dashes?
Convention only. UK banks print it as three pairs for readability, and forms normally accept it with or without the separators.