You need around a shot glass full amount or 30ml for a head-to-toe application.
Use the 2 Finger Rule, which is approximately 1/2 a teaspoon or 2.5ml:
2 Fingers = Face and neck
2 Fingers = Right Arm
2 Fingers = Left arm
4 Fingers = Front of body
4 Fingers = Back of body
4 Fingers = Right leg
4 Fingers - Left leg