Gross Rent Multiplier (GRM) = Purchase Price ÷ Annual Gross Rent. It's the fastest back-of-envelope way to screen deals since it ignores expenses entirely — a lower GRM generally means the price is more favorable relative to the rent it produces.
Because GRM ignores taxes, insurance, vacancy, and maintenance, it should only be used as an initial filter, not a final decision metric — two properties with the same GRM can have very different actual cash flow once real expenses are factored in via cap rate and cash-on-cash return.