Pre-Mix Gas Oil Ratio App. Cost $0.99 at the App Store
Gas Oil Mixture Ratio. Cost $0.99 at the App Store
Premix Calculator FREE at the App Store
If you are not an iPhone / Mac person, you can also check out this free calculator for your computer.
If you are filling a 5 US Gallon gas can with fuel, you can simply add 25.6 ounces or 3 1/4 cups of oil to the can to get a 25:1 mix ratio...don't use your wife's fancy measuring cups from the kitchen though!
If you have any tips or advice on mixing fuel for the Redcat Rampage or other 1/5 scale RC's, please leave a comment below and let everyone know about it.
Hope it helps.
Rob