The calcium absorption from vegetables is as good or better than that of milk. Calcium absorption from milk is approximately 32 percent. Figures for broccoli, brussels sprouts, mustard greens, turnip greens, and kale range between 40-64 percent. Beans are also rich in calcium.
Generally speaking, a rule of thumb to keep in mind is to make sure you’re eating enough beans and greens.
One exception to that rule is spinach, which contains a lot of calcium, but in a form that is difficult for the body to absorb.
The optimal calcium intake is unknown and differs a bit for everyone. Keep in mind, consuming meat and excess salt, using tobacco, and physical inactivity leads to rapid calcium loss.
When choosing calcium products, avoid calcium carbonate - it doesn’t absorb well. Instead, opt for calcium citrate and calcium hydroxyapatite.