This is a very subjective question as every candle maker has their own preference and it does vary according to the type of wax you are using as well as the potency of your fragrance oil, amongst other factors. We provide a fragrance load % indication within the wax specifications available. We recommend testing fragrance oils at 5% and adjusting from there. This means, if you are using 100g of wax, to use 5ml of oil to start with and increasing until you reach the desired strength. The maximum percentage would be 10%. Too much fragrance oil can cause colour bleed, reduce performance and increase the price of each candle so try not to add too much.