Is GRM the same as cap rate?

No. GRM is price divided by gross rent and ignores every expense. Cap rate is net operating income divided by price and includes vacancy, taxes, insurance, maintenance and management. GRM is a screen. Cap rate is the underwriting number.

The two are linked by the expense ratio. Cap rate is roughly (1 minus vacancy) times (1 minus expense ratio) divided by GRM. With 5% vacancy and expenses at 36% of collected rent, a GRM of 10 implies a cap rate near 6.1%. Change the expense ratio to 45% and the same GRM implies 5.2%.

A condo with $400 in monthly dues and a house with none can share a GRM of 10 while their cap rates sit two points apart. Use GRM to sort listings quickly, then compute cap rate on the survivors with their actual taxes, insurance and dues.