True-to-Size Millimeter Sizing Comparison
Sperry Billfish 3 Eye vs Sperry Saltwater
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 Billfish 3 Eye to see your calculated size in the Saltwater.
Complete Size Conversion Matrix
Direct millimeter-calibrated mapping comparing all available sizes between both shoes.
| Billfish 3 Eye (US) | Internal Cavity | Saltwater Equivalent | Match Accuracy | Fit Difference |
|---|---|---|---|---|
| US 7 | 267 mm | US 7 | 96% | +0.4 mm |
| US 7.5 | 270 mm | US 7.5 | 96% | +0.4 mm |
| US 8 | 273 mm | US 8 | 96% | +0.4 mm |
| US 8.5 | 277 mm | US 8.5 | 96% | +0.4 mm |
| US 9 | 280 mm | US 9 | 96% | +0.4 mm |
| US 9.5 | 283 mm | US 9.5 | 96% | +0.4 mm |
| US 10 | 287 mm | US 10 | 96% | +0.4 mm |
| US 10.5 | 290 mm | US 10.5 | 96% | +0.4 mm |
| US 11 | 293 mm | US 11 | 96% | +0.4 mm |
| US 11.5 | 297 mm | US 11.5 | 96% | +0.4 mm |
| US 12 | 300 mm | US 12 | 96% | +0.4 mm |
| US 12.5 | 303 mm | US 12.5 | 96% | +0.4 mm |
| US 13 | 307 mm | US 13 | 96% | +0.4 mm |
| US 14 | 313 mm | US 14 | 96% | +0.4 mm |
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Frequently Asked Questions
How does the Billfish 3 Eye size compare to the Saltwater?
Both shoes share a very similar length profile. We recommend ordering your standard size in both. The Billfish 3 Eye has an internal fit offset of 0.16mm compared to 0.52mm for the Saltwater.
Do these shoes fit wide feet comfortably?
The Billfish 3 Eye has a snug/narrow width profile, while the Saltwater is roomy/wide.