noun, plural ef·fi·cien·cies.

Is efficiency singular or plural?

The noun efficiency can be countable or uncountable. In more general, commonly used, contexts, the plural form will also be efficiency. However, in more specific contexts, the plural form can also be efficiencies e.g. in reference to various types of efficiencies or a collection of efficiencies.

What's the plural of efficiency?

ef·​fi·​cien·​cy | \ i-ˈfi-shən-sē \ plural efficiencies.