True-to-Size Millimeter Sizing Comparison
Reef Fanning vs Reef Reef Neptune
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 Fanning to see your calculated size in the Reef Neptune.
Complete Size Conversion Matrix
Direct millimeter-calibrated mapping comparing all available sizes between both shoes.
| Fanning (US) | Internal Cavity | Reef Neptune Equivalent | Match Accuracy | Fit Difference |
|---|---|---|---|---|
| US 3.5 | 240 mm | US 3.5 | 91% | +0.8 mm |
| US 4 | 243 mm | US 4 | 91% | +0.8 mm |
| US 4.5 | 247 mm | US 4.5 | 91% | +0.8 mm |
| US 5 | 250 mm | US 5 | 91% | +0.8 mm |
| US 5.5 | 253 mm | US 5.5 | 91% | +0.8 mm |
| US 6 | 257 mm | US 6 | 91% | +0.8 mm |
| US 6.5 | 260 mm | US 6.5 | 91% | +0.8 mm |
| US 7 | 267 mm | US 7 | 91% | +0.8 mm |
| US 7.5 | 270 mm | US 7.5 | 91% | +0.8 mm |
| US 8 | 273 mm | US 8 | 91% | +0.8 mm |
| US 8.5 | 277 mm | US 8.5 | 91% | +0.8 mm |
| US 9 | 280 mm | US 9 | 91% | +0.8 mm |
| US 9.5 | 283 mm | US 9.5 | 91% | +0.8 mm |
| US 10 | 287 mm | US 10 | 91% | +0.8 mm |
| US 10.5 | 290 mm | US 10.5 | 91% | +0.8 mm |
| US 11 | 293 mm | US 11 | 91% | +0.8 mm |
| US 11.5 | 297 mm | US 11.5 | 91% | +0.8 mm |
| US 12 | 300 mm | US 12 | 91% | +0.8 mm |
| US 12.5 | 303 mm | US 12.5 | 91% | +0.8 mm |
| US 13 | 307 mm | US 13 | 91% | +0.8 mm |
| US 14 | 313 mm | US 14 | 91% | +0.8 mm |
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Frequently Asked Questions
How does the Fanning size compare to the Reef Neptune?
Both shoes share a very similar length profile. We recommend ordering your standard size in both. The Fanning has an internal fit offset of -0.12mm compared to 0.68mm for the Reef Neptune.
Do these shoes fit wide feet comfortably?
The Fanning has a snug/narrow width profile, while the Reef Neptune is roomy/wide.