Number of Rows and Columns in Julia DataFrames

I have a Julia DataFrame:

df = DataFrame(a=1:4,b=5:8, c=["a", "b", "c", "d"])

4×3 DataFrame
 Row │ a      b      c      
     │ Int64  Int64  String 
─────┼──────────────────────
   1 │     1      5  a
   2 │     2      6  b
   3 │     3      7  c
   4 │     4      8  d

How do I get the number of rows an columns?