Brooks Glycerin 21 Sizing Guide: Does It Run Small or True to Size?

Fit Notes

ASICS GEL-Nimbus 26

The GEL-Nimbus 26 utilizes a highly elastic, stretchable upper that naturally accommodates foot swelling and feels inherently more forgiving. While standard sizing translates directly for most runners, individuals who prefer a roomy toe box should size up a half-size in the Glycerin 21 to counteract its stiff, heavily tapered toe bumper and less adaptable forefoot geometry.

Saucony Triumph 22

The Triumph 22 offers a springier underfoot ride and is noticeably wider throughout both the midfoot and the toe box. Standard-width runners with square-shaped feet will need to opt for a half-size larger in the Glycerin 21 to achieve a comparable level of forefoot comfort and toe splay. Note the compensation factor: if you typically size up in length solely to get extra width, you should instead opt for Brooks' dedicated wide widths (2E/4E) rather than extending the length, which can misalign the shoe's flex points.

Hoka Clifton 9

The Clifton 9 is engineered on a relatively narrow, highly rockered platform with a restrictive midfoot and arch architecture. Although the Glycerin 21 is functionally shorter in length due to its aggressive rearfoot padding, its midfoot volume is substantially more accommodating than the Hoka's narrow midsection, allowing most runners to stay true to their standard Hoka size while enjoying a more natural transition.

Brooks Ghost 16

As close relatives in the Brooks lineup, the Glycerin 21 delivers a softer, more cushioned ride and technically possesses a roomier baseline toe box than the Ghost 16. However, because the Glycerin 21 features a heavily padded heel collar that shunts the entire foot forward, runners who sit at the absolute upper limit of their size in the Ghost 16 must size up a half-size to maintain adequate longitudinal toe clearance.