as a rough guide , tare your scales if digital ( do this by sitting your container on scales - press tare. This will give you a zero balance , as the weight of the container is NOT include). Then add water to the container .... this will tell you roughly how many mls /grams it holds. Keep in mind that waxes and oils will have different densities , so there will be a slight variation , but it will give you something to work with . I have always beens told to go by weight rather than volume , so I use grams