Tap water is 10/Lbs gallon. the specific gravity is 1.000
5 Imp G=22.73 L
5 Us G = 18.92 L
22.73 L X 1.025 SG(saltwater) = 23.3 kg or 51.36 LBS
18.92 L X 1.025 Sg = 19.4 kg or 42.7 LBS
Then do the tare system Island reefer suggested. Zero the bucket out on a scale then fill it.
Hope it helps
