It would depend on the length of your stride.
3.5 feet
40' x 40' (1,600 square feet) = 177.7 sq. yards.
24,816 feet.
3 1/3 feet.
28 steps equal 100 feet
40 feet equals 12.192 meters.
3.5 feet in 42 inches.
Answer: 40 acres = 1,742,400 square feet.
42 feet = 12.8016 meters.
13.33 yards.
12,190 mm
3.33 repeating