True-to-Size Millimeter Sizing Comparison
Allbirds Tree Runner vs ASICS GEL-Nimbus 27
Detailed size conversion chart, cavity measurements in millimeters, and crowd-sourced fit advice for choosing your perfect size.
Interactive Size Converter
Select what size you wear in the Tree Runner to see your calculated size in the GEL-Nimbus 27.
Complete Size Conversion Matrix
Direct millimeter-calibrated mapping comparing all available sizes between both shoes.
| Tree Runner (US) | Internal Cavity | GEL-Nimbus 27 Equivalent | Match Accuracy | Fit Difference |
|---|---|---|---|---|
| US 3.5 | 240 mm | US 4 | 87% | +1.1 mm |
| US 4 | 243 mm | US 4.5 | 63% | +3.1 mm |
| US 4.5 | 247 mm | US 5 | 51% | +4.1 mm |
| US 5 | 250 mm | US 5 | 87% | +1.1 mm |
| US 5.5 | 253 mm | US 5.5 | 63% | +3.1 mm |
| US 6 | 257 mm | US 6 | 51% | +4.1 mm |
| US 6.5 | 260 mm | US 6 | 87% | +1.1 mm |
| US 7 | 267 mm | US 7 | 81% | +1.6 mm |
| US 7.5 | 270 mm | US 7.5 | 87% | +1.1 mm |
| US 8 | 273 mm | US 8 | 63% | +3.1 mm |
| US 8.5 | 277 mm | US 8.5 | 51% | +4.1 mm |
| US 9 | 280 mm | US 8.5 | 87% | +1.1 mm |
| US 9.5 | 283 mm | US 9 | 63% | +3.1 mm |
| US 10 | 287 mm | US 9.5 | 51% | +4.1 mm |
| US 10.5 | 290 mm | US 9.5 | 87% | +1.1 mm |
| US 11 | 293 mm | US 10 | 63% | +3.1 mm |
| US 11.5 | 297 mm | US 10.5 | 81% | +1.6 mm |
| US 12 | 300 mm | US 11 | 87% | +1.1 mm |
| US 12.5 | 303 mm | US 11.5 | 63% | +3.1 mm |
| US 13 | 307 mm | US 12 | 51% | +4.1 mm |
| US 14 | 313 mm | US 12.5 | 63% | +3.1 mm |
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Frequently Asked Questions
How does the Tree Runner size compare to the GEL-Nimbus 27?
Both shoes share a very similar length profile. We recommend ordering your standard size in both. The Tree Runner has an internal fit offset of -0.2mm compared to -0.08mm for the GEL-Nimbus 27.
Do these shoes fit wide feet comfortably?
The Tree Runner has a snug/narrow width profile, while the GEL-Nimbus 27 is snug/narrow.