A D crochet hook, also written D-3, is 3.25mm. This is one of the letters I get asked about often, since patterns list the letter but hooks are usually easiest to double check by mm.
D hook in mm, and what it’s used for
At 3.25mm, a D hook matches sport weight yarn. In UK and Canadian sizing, the same hook is a 10, and I always convert by mm rather than assume a UK number lines up with a US letter.
How D compares to nearby letters
There is no standard lettered size directly below this one on the chart. A E-4 hook goes one step larger, giving a looser drape. I pick between them based on whether the project needs structure or drape.
Frequently asked questions
Is D-3 the same as 3.25mm?
Yes, D and D-3 both refer to the same 3.25mm hook in US sizing. I use the two names interchangeably myself.
What yarn weight is a D hook for?
Sport weight yarn is the standard match for a D hook, and it is the pairing I reach for first.
See the full hook size chart
Compare D against every other letter, mm, and UK size in one table.