The most common and most likely answer to this crossword clue is the 5 letter word GIRTH
I've seen this crossword clue in The Daily Telegraph
G
I
R
T
H
More clues leading to the result GIRTH
- Saddle band? Get it round the horse at first
- Hard bit of maths — set about finding measurement
- Saddle strap, right when adjusted
- Size may be right when altered
- Measure right round
- Size of waist perhaps taking cook aback
- Right to change horse’s strap
- Equipment put round most of the perimeter
- Sort out right measurement for trousers?
- It’s right to alter measure of thickness
Buddy explains!

The straight part
We know that "measurement for trousers?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case measurement for trousers? = girth.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GIRTH mean?
GIRTH noun- A band passed under the belly of an animal, which holds a saddle or a harness saddle in place.
- The part of an animal around which the girth fits.
- One's waistline circumference, most often a large one.
- A small horizontal brace or girder.
- The distance measured around an object.
- The length of the shortest cycle in a graph.
- To bind as if with a girth or band.