Picking the right oar length is one of the most important parts of setting up a comfortable and efficient oar boat. A well-sized oar lets you row smoothly, maintain control in pushy water, and stay strong through long days on the river.
Some boaters rely on the 1:2 ratio “⅓ inboard / ⅔ outboard” rule to size their oars. It’s simple, easy to visualize, and gets you close. But close isn’t the same as ideal.
A Better Ratio 11:27
A more efficient setup uses an 11:27 ratio — meaning 11 parts of the oar length are inboard and 27 parts are outboard. This works out to roughly 29% inboard and 71% outboard, giving you:
- Better leverage,
- A more natural hand position,
- Less fatigue, and
- Cleaner blade entry and exit on every stroke.
Using the 1.63 Formula for Oar Length
After years of rowing and rigging rafts, I’ve found a simple, fast way to calculate proper oar length:
This 1.63 multiplier builds in the 11/27 ratio, so you end up with the right balance between inboard and outboard from the start.
Example:
If your raft is 66 inches wide at the oarlocks:
- 66 × 1.63 = 107.6 inches
- 107.6 ÷ 12 ≈ 9 feet
That means a 9-foot oar is a great fit. If your raft tubes are big and/or you have great oar management you can bump it up half a foot to 9' 6" oars. If you're oar management is weak or you are worried about the strain of longer oars on your shoulders then drop off half a foot to 8' 6" oars.
Setting Your Oar Stops
Once you’ve chosen your oar length, set your oar stops or clips to match the 11/27 ratio.
For a 9-foot oar:
- Total length = 108 inches
- Inboard = 108 x 11 / 38 ≈ 31 inches
- Outboard = 108 x 27 / 38 ≈ 77 inches
For a 10-foot oar:
- Inboard ≈ 34.5 inches
- Outboard ≈ 85.5 inches
This creates a comfortable handle spread, smooth rowing strokes, and efficient leverage.
Quick Reference Chart
| Width at Oarlocks | Recommended Oar Length |
|---|---|
| 48 in | 8 ft |
| 54 in | 8.5 ft |
| 60 in | 9 ft |
| 66 in | 9–9.5 ft |
| 72 in | 10 ft |
| 78 in | 10.5 ft |
| 84 in | 11 ft |
This chart gives you a solid starting point, but you can fine-tune depending on seat height, tube diameter, oar management, and personal rowing style.
Final Thoughts
The ⅓ inboard / ⅔ outboard rule will get you on the water, but if you want to row more efficiently and comfortably, the 11/27 ratio is a better approach. Using the 1.63 multiplier is a quick way to get the right sized oar.
A properly balanced oar setup means less strain, better boat control, and a lot more fun on the water.
