The Cap Rate – Capitalization Rate – is the rate that the investment returns and it is calculated by: annual net income / cost
Gross rent multiplier is the gross annual rent income divided by price.
It is almost like the inverse of the gross rent multiplier GRM, except that the gross rent multiplier is the gross rent and the cap rate is the net rental income.
If you are looking for a higher CAP Rate then look for a lower GRM.
Assuming that the gross rental income is the same as the net rental income (tenants pay for all expenses):
If an investor bought a 4-plex for $1,000,000 and each unit rental income is $1200 a month, so total income is $4,800 a month, or $57,600 a year ($4800 a month x 12)
CAP Rate : $57,600 / $1,000,000 = 5.76%
Gross Rent Multiplier GRM = 1,000,000 / $57,600 = 17.63
Some people calculate a monthly GRM (and post on MLS as GRM) : 1,000,000 / $4800 = 211
If you are looking for specific cap rate or GRM, then add GRM to your MLS search. Not every realtor add this info though, and some add the monthly in the same field.
The other way you can do is to search by ranges. Different searches with price ranges and rental income ranges.
Some areas have higher GRM. Normally, where home prices per sqft are lower, GRM tend to be lower too. Maybe there is an expectancy that the the home prices and/or rental income will go up faster on higher priced areas.