According to National Institute of Health, it's better to use smaller calcium supplements. Taking a single 1000 mg pill is not productive. You're better off taking two smaller pills at different times of the day.

"The percentage of calcium absorbed from supplements, as with that from foods, depends not only on the source of calcium but also on the total amount of elemental calcium consumed at one time; as the amount increases, the percentage absorbed decreases. Absorption from supplements is highest with doses of 500 mg or less. For example, the body absorbs about 36% of a 300 mg calcium dose and 28% of a 1,000 mg dose."