Calcium oxalate is a chemical compound that forms needle-shaped crystals. Its chemical formula is CaC2O4 or Ca(COO)2.

Oxalate or ethanedioate is the divalent anion with formula C2O42− or (COO)22−, resulting from oxalic acid by loss of two protons. Either name is often used for a salt containing this anion (such as disodium oxalate, (Na+)2C2O42−), or an ester of oxalic acid (such as dimethyl oxalate, (CH3)2C2O4).

It has chemical formula K2C2O4.

Disodium oxalate, often called simply sodium oxalate, is a sodium salt of oxalic acid with the molecular formula Na2C2O4. It is usually a white, crystalline, odorless powder, that decomposes at 250–270 °C.