Manhattan street addresses follow an algorithm that allows anyone with rudimentary math skills and the following charts to find
the nearest cross street for a house number on an avenue.
Take the number of the street address, drop the last digit, divide by two (essentially dividing the address by 20 but accounting for odd numbers), and add or subtract the number in the chart. For example, 945 Madison Avenue (Whitney Museum of American Art, by the way) would yield the following equation:
945 / 2 = 47 + 27 (from the chart below) = 74th Street.
*The entrance is actually closer to 75th Street, but the museum takes up the whole block so it is just as close to 74th Street.
Avenues A, B, C, D: add 3
1st Avenue: add 3
2nd Avenue: add 3
3rd Avenue: add 10
4th Avenue: add 8
5th Avenue
63 - 108: add 11
109 - 200: add 13
201 - 400: add 16
401 - 600: add 18
601 - 775: add 20
776 - 1286: divide by 10 (instead of 20), subtract 18
1287-1500: add 45
1501 - 2000: add 24
Avenue of the Americas (6th Avenue): subtract 12
7th Avenue
1 - 1800: add 12
1801 and up: add 20
8th Avenue: add 9
9th Avenue: add 13
10th Avenue: add 14
11th Avenue: add 15
Amsterdam Avenue: add 59
Audubon Avenue: add 165
Broadway
1-754: unnumbered streets, south of 8th Street
756 - 846: subtract 29
847 - 953: subtract 25
above 953: subtract 31
Central Park West: divide by 10 (not 20), add 60
Columbus Avenue: add 60
Lenox Avenue: add 110
Lexington Avenue: add 22
Madison Avenue: add 27
Manhattan Avenue: add 100
Park Avenue: add 35
Park Avenue South: add 8
Pleasant Avenue: add 101
St. Nicholas Avenue: add 110
Riverside Drive
1 - 567: divide by 10 (not 20), add 72
above 567: divide by 10 (not 20), add 78
Wadsworth Avenue add 173
West End Avenue: add 60
York Avenue: add 4