I'm assuming its a two stroke petrol one. Most chainsaws, disc cutters etc run at 50:1, but how we used to do it on site was to put a capful of oil in, then fill it with petrol. Always used to work.
You should check on your handbook as the chainsaw I use takes a 20:1 mix a strimmer I use takes a 25:1 mix and I know that most disc cutters use 50:1 The important thing to remember is that you do put the two stroke in as it will work without oil in but not for very long!!