Should I size up in the Brooks Glycerin 21 for thick socks or break-in?

Break-in: None. Thick socks add volume — try the sock you will wear with the usual size advice before jumping a full size. See the thick socks & boot break-in guides.

How do women’s sizes work for the Brooks Glycerin 21?

Open Women’s sizing for this model at /womens/brooks/glycerin-21/ for the brand’s men’s↔women’s gap plus this model’s fit offset. Do not assume every brand uses a 1.5 gap.

How does the Brooks Glycerin 21 compare to the Ghost 16?

Same brand, different last. Glycerin 21: True to Size — True to size. Ghost 16: true to size — True to size — use Brooks widths if you need them. Open /brooks/ghost-16/ or a model compare when available.

Brooks Glycerin 21 Size: True to Size Daily Trainer

Partial · methodology

True to Size True to size

PartialLast reviewed 2026-08-11

Runs smallTrue to sizeRuns big

Length usually matches a typical street size for this category.

Width note: Plush midsole â€” length usually TTS

What size should you buy?

Your usual size

Interactive suggestion based on this model’s fit offset (+0 US). Always confirm with a retailer return policy.

Brand / model converter · Compare brands · Guides

Measured / size chart (cm)

Numbers only when sourced. Empty fields stay blank — we do not invent mm.

Brooks size chart (foot-length cm)
US M	UK	EU	cm
6	5.5	38.5	23.5
6.5	6	39	24
7	6.5	40	24.5
7.5	7	40.5	25
8	7.5	41	25.4
8.5	8	42	25.9
9	8.5	42.5	26.2
9.5	9	43	26.7
10	9.5	44	27.1
10.5	10	44.5	27.5
11	10.5	45	27.9
11.5	11	45.5	28.4
12	11.5	46	28.8
13	12.5	47.5	29.7

Chart cm is approximate foot length for label matching — not a lab internal cut. Use the cm converter to map foot length across brands.

Width: Plush midsole â€” length usually TTS
Break-in: None

Summary

Glycerin usually matches Ghost-style TTS length with a plush ride. Prioritize correct width over length tricks. Soft foam can make the shoe feel roomier underfoot without changing labeled size needs.

Sources: Brooks Glycerin TTS / width ladder · Glycerin vs Ghost volume · Daily-trainer toe-room guidance · methodology

Women’s sizing

Brooks uses a 1.5-size women’s→men’s US gap (not always 1.5). Convert your women’s US size with this model’s fit offset built in.

Women’s size in Glycerin 21 · All brands

What size did you take?

Anonymous fit check for Brooks Glycerin 21. Helps future readers — we never invent crowd stats.

Community results stay private until 25 responses for this page — no fake percentages.

Prefer email? Fit feedback.

FAQ

Does the Brooks Glycerin 21 run big or small?: True to Size. True to size Glycerin usually matches Ghost-style TTS length with a plush ride. Prioritize correct width over length tricks. Soft foam can make the shoe feel roomier underfoot without changing labeled size needs.
What size should I buy in the Brooks Glycerin 21?: True to size
Should I size up in the Brooks Glycerin 21 for thick socks or break-in?: Break-in: None. Thick socks add volume — try the sock you will wear with the usual size advice before jumping a full size. See the thick socks & boot break-in guides.
How do women’s sizes work for the Brooks Glycerin 21?: Open Women’s sizing for this model at /womens/brooks/glycerin-21/ for the brand’s men’s↔women’s gap plus this model’s fit offset. Do not assume every brand uses a 1.5 gap.
How does the Brooks Glycerin 21 compare to the Ghost 16?: Same brand, different last. Glycerin 21: True to Size — True to size. Ghost 16: true to size — True to size — use Brooks widths if you need them. Open /brooks/ghost-16/ or a model compare when available.

Generic US / UK / EU / cm reference

Secondary Mondopoint-style table. Prefer the brand chart in Measured / size chart (cm) when converting. Primary system: US_M.

US	UK	EU	cm
6	5.5	39	24.0
6.5	6	39.5	24.5
7	6.5	40	25.0
7.5	7	40.5	25.5
8	7.5	41	26.0
8.5	8	42	26.5
9	8.5	42.5	27.0
9.5	9	43	27.5
10	9.5	44	28.0
10.5	10	44.5	28.5
11	10.5	45	29.0
11.5	11	45.5	29.5
12	11.5	46	30.0
13	12.5	47.5	31.0

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Glycerin 21 sizing: true to size like Ghost