True-to-Size Millimeter Sizing Comparison
Spring Step Happy vs Spring Step Orella
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 Happy to see your calculated size in the Orella.
Complete Size Conversion Matrix
Direct millimeter-calibrated mapping comparing all available sizes between both shoes.
| Happy (US) | Internal Cavity | Orella Equivalent | Match Accuracy | Fit Difference |
|---|---|---|---|---|
| US 3.5 | 239 mm | US 3.5 | 99% | +0.1 mm |
| US 4 | 242 mm | US 4 | 99% | +0.1 mm |
| US 4.5 | 246 mm | US 4.5 | 99% | +0.1 mm |
| US 5 | 249 mm | US 5 | 99% | +0.1 mm |
| US 5.5 | 252 mm | US 5.5 | 99% | +0.1 mm |
| US 6 | 256 mm | US 6 | 99% | +0.1 mm |
| US 6.5 | 259 mm | US 6.5 | 99% | +0.1 mm |
| US 7 | 266 mm | US 7 | 99% | +0.1 mm |
| US 7.5 | 269 mm | US 7.5 | 99% | +0.1 mm |
| US 8 | 272 mm | US 8 | 99% | +0.1 mm |
| US 8.5 | 276 mm | US 8.5 | 99% | +0.1 mm |
| US 9 | 279 mm | US 9 | 99% | +0.1 mm |
| US 9.5 | 282 mm | US 9.5 | 99% | +0.1 mm |
| US 10 | 286 mm | US 10 | 99% | +0.1 mm |
| US 10.5 | 289 mm | US 10.5 | 99% | +0.1 mm |
| US 11 | 292 mm | US 11 | 99% | +0.1 mm |
| US 11.5 | 296 mm | US 11.5 | 99% | +0.1 mm |
| US 12 | 299 mm | US 12 | 99% | +0.1 mm |
| US 12.5 | 302 mm | US 12.5 | 99% | +0.1 mm |
| US 13 | 306 mm | US 13 | 99% | +0.1 mm |
| US 14 | 312 mm | US 14 | 99% | +0.1 mm |
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Frequently Asked Questions
How does the Happy size compare to the Orella?
Both shoes share a very similar length profile. We recommend ordering your standard size in both. The Happy has an internal fit offset of -1mm compared to -0.88mm for the Orella.
Do these shoes fit wide feet comfortably?
The Happy has a snug/narrow width profile, while the Orella is roomy/wide.