Ethanol Content Estimator
The BuildLockr ethanol content estimator helps you calculate your true fuel mix from a physical sample. Use this tool to calculate your exact E85 percentage after doing a water separation test. Whether you use a graduated test tube or measure direct volumes, this E85 ratio calculator gives you the true ethanol rating. This helps drivers tune safely by knowing exactly what is in their gas tank.
Graduated Test Tube Method
Ethanol % = ((Separation Mark - Water Added) ÷ Fuel Sample) × 100
Input the exact values read directly from your graduated ethanol test bottle/cylinder. The tool automatically isolates the added water to find the true fuel percentage.
Scratchpad / Quick Notes
* Note: This scratchpad is temporary and will be cleared when you leave or refresh the page.
Comparison Log & Run History
No calculations logged yet.
Perform a calculation and click "Log Current Run" to save it for side-by-side comparison.
* Runs are stored temporarily in your active session and will be cleared when you leave this page.
Quick-Swap Unit Converter
How to Estimate Ethanol Content
- Using a graduated test tube, add water up to the first marked line (e.g. 10 ml).
- Add your fuel sample up to the top marked line (e.g. 100 ml total).
- Shake the mixture vigorously for 10-15 seconds.
- Let it settle on a flat surface for 1-2 minutes until phase separation is complete.
- Read the volume of the water-ethanol separation line. Calculate using the tool above!
Common Ethanol Content Questions
Why is E85 content important?
Pump E85 content can vary from 51% to 85% depending on the season (winter blends have less ethanol) and region. If your tune expects 85% but you get 51%, your engine may run poorly or knock. Always test your fuel.