What is "quantum meruit"

Quantum \Quan"tum\, n.; pl. Quanta. [L., neuter of quantus how great, how much. See Quantity,]

1. Quantity; amount. ``Without authenticating . . . the quantum of the charges.''
   --Burke.

2. (Math.) A definite portion of a manifoldness, limited by a mark or by a boundary.
   --W. K. Clifford.

   Quantum meruit[L., as much as he merited] (Law), a count in an action grounded on a promise that the defendant would pay to the plaintiff for his service as much as he should deserve.

   Quantum sufficit, or Quantum suff. [L., as much suffices] (Med.), a sufficient quantity; -- abbreviated q. s. in pharmacy.

   Quantum valebat[L., as much at it was worth] (Law), a count in an action to recover of the defendant, for goods sold, as much as they were worth.
   --Blackstone.

n. (context legal English) an inference that the defendant has promised to pay the plaintiff for the plaintiff's work or labor as much as he should deserve

Quantum meruit is a Latin phrase meaning "what one has earned". In the context of contract law, it means something along the lines of "reasonable value of services".

In the United States, the elements of quantum meruit are determined by state common law. For example, to state a claim for unjust enrichment in New York, a plaintiff must allege that (1) defendant was enriched; (2) the enrichment was at plaintiff's expense; and (3) the circumstances were such that equity and good conscience require defendants to make restitution.