5987. To Find the Square Surface or Area of a Circle

5987.    To Find the Square Surface or Area of a Circle. Square the radius (half the diameter), and multiply that by 3.14159; for small calculations 31/7 is nearly the same as 3.14159. Thus, to find the area of a circle whose diameter is 8 feet: The radius is 4 feet, this squared is 16; then 16 times 3.14159 is 50.265 square feet. If the diameter is 8 inches, the area would be 50.265 square inches.

5988. Table Showing the Square Inches Contained in a Circle from Ten to Seventy-Three Inches in Diameter

5988.      Table Showing the Square Inches Contained in a Circle from Ten to Seventy-Three Inches in Diameter.

Diameter of Circle.

Square Inches.

Diameter of Circle.

Square Inches.

10

78.54

42

1388.59

11

95.03

43

1452.20

12

113.10

44

1520.53

13

132.73

45

1590.43

14

153.94

46

1661.91

15

176.71

47

1735.00

16

201.06

48

1809.56

17

226.98

49

1885.74

18

254.47

50

1963.50

19

283.54

51

2042.82

20

314.16

52

2123.72

21

346.36

53

2206.19

22

380.13

54

2290.23

23

415.47

55

2375.83

24

452.39

56

2463.00

25

490.88

57

2551.76

26

530.93

58

2642.00

27

572.56

59

2734.00

28

615.75

60

2827.44

29

660.20

61

2922.47

30

706.86

62

3019.00

31

754.77

63

3117.25

32

804.25

64

3217.00

33

855.30

65

3318.31

34

907.92

66

3421.20

35

962.00

• 67

3526.66

36

1017.88

68

3651.69

37

1075.20

69

3739.29

38

1134.00

70

3848.46

39

1194.60

71

3959.20

40

1256.64

72

4071.51

41

1320.26

73

4185.40

The area may also be obtained by multiplying the square of the diameter by .7854. This method is deduced from the first one, and is founded on the fact that the square of any number is always 4 times as much as the square of half the number. In the first method the radius or half diameter is to be squared, and multiplied by 3.14159; in the second, the whole diameter is squared, which will result in just 4 times as much as the square of the radius; the multiplier must be therefore the fourth part of 3.14159, or .7854.