How Do I Mix Fuel for My String Trimmer, Hedge Trimmer or Chainsaw?

These garden power tools generally have a two stroke engine (also known as a two cycle or 2T engine), and to make them lighter, they don't carry motor oil on board as in the case of a lawn mower or road vehicle. Instead oil is added and mixed with the petrol (gas) before use.
In general petrol/oil ratio for 2-stroke engines is 40:1 or 50:1 which is 2.5% or 2% oil. 50:1 is equivalent to 20ml in 1 litre or just over 2 1/2 US fluid ounces per US gallon. 40:1 is equivalent to 25ml in 1 litre or 3.2 US fluid ounces per US gallon. 
After adding oil, swirl the contents around to ensure it's thoroughly mixed.Consult the manual of the machine for details of the recommended ratio.