Thats how its always worked out for me,and if you get a single rep with a weight,then increase it to 2 reps your maximum will have risen roughly 10lbs.so if you get 3 reps with 3 plates you will get 1 rep with 3 plates and 5kg,you get 5 reps with 3 plates you get 1 rep with 3 and a half plates,you get 7-8 reps with 3 plates you get 1 rep with 3 plates and 15kg,all the way up to 10 reps equals 1 rep with 4 plates.Keep in mind i`m talking euorpean weight are in kilos,so a 20kg jump each side is 40kg(88lbs),and thats why i say when you increase your 1 rep max by one rep your strength will have gone up 10lbs.