Weights without scales

I have a 1kg box of moss killer I need to mix it at 120g per 10 litres. I have no scales.

1. Assume the box is full. It measures 6x13x21 cm or 1638 cm3
2. I need 0.12 of a box or 196.56 cm3
3. I have a roughly cylindrical jug of diameter 12.5 cm
4. The bottom of the jug therefore has an area of 122.71 cm2
5. I therefore need to fill the jug to the 1.6 cm line

Or I could just go and buy some scales, but where's the fun in that?