The recommended amount of calcium for women age 51 and older and for men age 71 and older is 1200 mg daily; for women age 19-50 the amount is 1000 mg; and for men age 19-70 the amount is 1000 mg. Check the chart in the link for those who are pregnant or lactating or younger than 19. Figure out how much you are getting from food, and then supplement the rest, but try to get most of it from food. Try not to take more than about 500 mg calcium at a time because that is about the most you can absorb.
Separate your calcium and strontium by at least three hours because calcium will reduce the absorption of strontium. The amount of calcium to take does not vary with the amount of strontium you are taking, just be sure to take both at separate times. The total amount of calcium needed depends on your age, sex, and whether you are pregnant or lactating. There is no adjustment for weight except what is already built into the calcium recommendations, which are much lower for infants and very young children. The amount of calcium to supplement depends on how much you are getting from your diet.