Will be 1 part oil to 100 parts petrol.
So if theirs 1000ml in a litre ( i think), it would be 10ml that you needed to add to one litre of petrol.
10ml oil to 1 litre of petrol
Usually theirs a chart on the side of the 2 stroke oil bottle to help.
Please wait for a few replies before you try out my reconings, so I can be told if I,m right or wrong.