Either of these three, with the topmost best.
25.4mm margin, with a minimum stave space of 0.925mm (3.7mm for a full stave), or, more commonly, 1.75mm stave space (7mm for a full stave).
Or, depending on the work, refer to these rastral numbers:
Rastral # : mm/stave
0 : 9.2
1 : 7.9
2 : 7.4
3 : 7
4 : 6.5
5 : 6
6 : 5.5
7 : 4.8
8 : 3.7
Comments
Depends on the genre of music and what country you are in.
Any of those available in layout/page size.
A3: 420 x 297mm
B4: 353 x 250mm
A4: 297 x 210mm
Either of these three, with the topmost best.
25.4mm margin, with a minimum stave space of 0.925mm (3.7mm for a full stave), or, more commonly, 1.75mm stave space (7mm for a full stave).
Or, depending on the work, refer to these rastral numbers:
Rastral # : mm/stave
0 : 9.2
1 : 7.9
2 : 7.4
3 : 7
4 : 6.5
5 : 6
6 : 5.5
7 : 4.8
8 : 3.7