Usage always depends on the type of canvas.
The cotton tent canvas of a trailer tent for example, will always absorb more shampoo than the fabric of a boat cover, which also contains plastic.
On average you can continue with the usage below.
1 liter = 6 to 14 m²
By first cleaning the fabric with normal lukewarm water, it is already saturated with water. Then spray the Sprayhood & Tent Shampoo onto the tent canvas. It will then be easier to absorb.