Listed gear-ratio data for 2025 Mercury 9.9 HP FourStroke outboards. Match your exact model and lower unit; some models may have more than one gearcase configuration.
2025 Mercury 9.9 HP FourStroke
Listed ratio values: 2.08:1
| Model | Gear ratio |
|---|---|
| 2005-UP | 2.08:1 |
Use the ratio that matches your exact outboard model and lower unit, then enter it in the PropSlip calculator.