There is no fixed dosage; a moderate amount is a good starting point. The typical method is to dilute about 1-2 tablespoons of the liquid in a separate container of water, then pour or ladle this mixture directly onto your sauna heater's hot rocks (if they are designed for water use). The intense heat instantly vaporises the water and carries the essential oils into the steam. This is the most effective way to scent the entire space. You can also pour the diluted mixture onto the floor or benches, but the aromatic release will be slower and more localised.
Important safety notes: Never pour the undiluted concentrate directly onto hot rocks, as this can cause spattering or produce a very intense, potentially overwhelming fragrance. For electric sauna stoves or hot plates, check your unit's manual; some are not designed for water at all. In a steam room or shower, you can add the diluted solution to the steam generator inlet or onto the floor where hot water runs. Always start with a smaller amount, especially if you are sensitive to scents, and add more later if desired. Avoid getting the liquid in your eyes.