Although the two are often confused and melded together, quantum meruit and unjust enrichment are distinct legal theories which can form the basis for a lawsuit. In practice, they are often pleaded and argued together; however, they have different measures of damages.
Quantum meruit requires that the plaintiff prove: (1) he provided the defendant with materials/services at the defendant’s request or with the acquiescence of the defendant, (2) that the materials had a reasonable value, and (3) that the defendant failed and refused to pay the reasonable value of such materials/services despite the demands of plaintiff.
For unjust enrichent, the plaintiff must prove (1) the defendant was enriched by a receipt of a benefit, (2) the enrichment was at the expense of the plaintiff and (3) it would be unjust to allow the defendant to retain the benefit.
The critical distinction is that quantum meruit awards money damages based on the reasonable value of the goods or services. This usually requires some expert testimony or proof of the fair market value of the goods or services. Unjust enrichment, on the other hand, measures damages not by the amount of the enrichment — but by the amount of the enrichment for which it would be unjust for defendant to retain.
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