Calcium hydride is the chemical compound with the formula CaH₂, an alkaline earth hydride. This grey powder (white if pure, which is rare) reacts vigorously with water, liberating hydrogen gas. CaH₂ is thus used as a drying agent, i.e. a desiccant.

CaH₂ is a saline hydride, meaning that its structure is salt-like. The alkali metals and the alkaline earth metals heavier than beryllium all form saline hydrides. A well-known example is sodium hydride, which crystallizes in the NaCl motif. These species are insoluble in all solvents with which they do not react. CaH₂ crystallizes in the PbCl₂ (cotunnite) structure.

Calcium hydride is prepared from its elements by direct combination of calcium and hydrogen at 300 to 400 °C.

CaH₂ is a reducing agent for the production of metal from the metal oxides of Ti, V, Nb, Ta, and U. It is proposed to operate via its decomposition to Ca metal:

CaH₂ has been used for hydrogen production. In the 1940s, it was available under the trade name "Hydrolith" as a source of hydrogen:

The trade name for this compound is "hydrolith"; in cases of emergency, it can be used as a portable source of hydrogen, for filling airships. It is rather expensive for this use.

The reference to "emergency" probably refers to wartime use. The compound has, however, been widely used for decades as a safe and convenient means to inflate weather balloons. Likewise, it is regularly used in laboratories to produce small quantities of highly pure hydrogen for experiments. The moisture content of diesel fuel is estimated by the hydrogen evolved upon treatment with CaH₂.

The reaction of CaH₂ with water can be represented as follows: