The United Kingdom does not use a grade point average. A UK degree ends in a classification: first class, upper second, lower second or third, awarded on a weighted average of percentage marks under rules each institution sets in its own regulations. Converting between a classification and a grade point average is therefore a mapping between two different systems rather than a calculation, and every mapping belongs to a named body.
What a UK classification is
A UK degree is classified into a first, an upper second, a lower second or a third on a weighted average of percentage marks. The boundaries between those classes, the weighting between years of study, the treatment of borderline cases and any discounting of the weakest module are set in each institution's own academic regulations rather than nationally. That is why two students with identical marks at different universities can classify differently, and why a boundary quoted without an institution's name attached is not a rule anyone applies.
Why it does not convert arithmetically
A grade point average is an average of letters mapped to points; a classification is a band on an average of percentages. Neither derives from the other. Any conversion is an assertion by a named body: a receiving university's admissions page, a recognised credential evaluator, or a national agency. Those bodies publish different mappings and do not always agree with each other.
What to do with an American transcript
Ask the UK institution which conversion it applies before doing any arithmetic. Most publish an equivalence for common grade point averages on their international admissions pages, and that published figure is the one that will be used to assess the application, whatever a general conversion table says.
Questions people ask about uk grading system
What is the UK equivalent of a 3.5 GPA?
There is no single answer. Receiving institutions and credential evaluators publish their own equivalences and they differ, so the one that counts is whichever the institution assessing your application uses.
Does the UK use a GPA?
Not for degree classification. UK degrees end in a class, awarded on a weighted average of percentage marks under each institution's own regulations. Some UK institutions publish a grade point average alongside for international purposes.
Is there a national percentage for a first class degree?
No. Each institution sets the class boundaries, the weighting between years and the treatment of borderline cases in its own academic regulations. A figure quoted without an institution's name attached is a convention rather than a rule.