This APP has three different calculators for people who want to use ethanol mixtures in their cars.

Refill calculator:
It's for daily use in gas station to easily calculate how much you need E85 and petrol to get desired ethanol content.

E% calculator:
It gives the answer for ethanol content when E85 and petrol amounts are known. Total amount and mixture percentages are also provided.

Mix calculator:
It gives the answer for E85 and petrol amounts when total amount and desired ethanol content is known.

To get accurate blends one needs to know what is the ethanol content in local gas station in E85 and petrol.