DAFI 36-2903 sets no single length limit for men; it caps bulk at 2 1/2 inches, with hair tapered to 1/4-inch at the natural termination point and only closely cut or shaved hair allowed to touch the collar. The same rule governs Space Force Guardians — the instruction applies to both services.
Air Force men's hair standards are set by DAFI 36-2903, paragraph 3.1.2. The instruction does not give a length in inches; it controls hair through shape, taper and bulk instead.
Tapered appearance on both sides and the back of the head, both with and without headgear so that when viewed from any angle the member's hair conforms to the shape of the head, curving inward to the natural termination point without eccentric directional flow, twists, or spiking.
DAFI36-2903, para 3.1.2
The bulk limit and the collar rule follow directly after:
Hair will not exceed 2 ½ inches in bulk, regardless of length and 1/4-inch at natural termination point; allowing only closely cut or shaved hair on the back of the neck to touch the collar
DAFI36-2903, para 3.1.2
Bulk is measured out from the scalp, not length along a hair strand, which is why a high-and-tight and a longer tapered cut can both be in standard as long as neither exceeds 2 1/2 inches of bulk and the hair still tapers to 1/4 inch at its natural termination point.
A general rule in paragraph 3.1.1 applies on top of the male-specific one: hair must not touch either eyebrow or extend below an imaginary line across the forehead at the top of the eyebrows.
This standard applies equally to Space Force Guardians. DAFI 36-2903 governs both services, and its own applicability section says references to Airmen and Air Force terminology extend to Guardians and the Space Force unless the Space Force issues separate guidance — which, for hair standards, it has not.