Tempera ture Conversions High Tempera tures Judged by Color Colors for Tempering To Find Circumference • Multiply diameter by 3.1416 • Or divide diameter by 0.3183 To Find Diameter • Multiply circumference by 0.3183 • Or divide circumference by 3.1416 To Find Radius • Multiply circumference by 0.15915 • Or divide circumference by 6.28318 To Find Side of an Inscribed Square • Multiply diameter by 0.7071 • Or multiply circumference by 0.2251 • Or divide circumference by 4.4428 To Find Side of an Equal Square • Multiply diameter by 0.8862 • Or divide diameter by 1.1284 • Or multiply circumference by 0.2821 • Or divide circumference by 3.545 Square • Asidemultipliedby1.4142equalsdiameterofitscircumscribingcircle • A side multiplied by 4.443 equals circumference of its circumscribing circle • A side multiplied by 1.128 equals diameter of an equal side • A side multiplied by 3.547 equals circumference of an equal circle To Find the Area of a Circle • Multiply circumference by one-quarter of the diameter • Or multiply the square of diameter by 0.7854 • Or multiply the square of circumference by .07958 • Or multiply the square of 1/2 diameter by 3.1416 To Find the Surface of a Sphere or Globe • Multiply the diameter by the circumference • Or multiply the square of a diameter by 3.1416 • Or multiply four times the square of radius by 3.1416 ˚F = ˚C x 9 + 32 5 ˚C = ˚F - 32 x 5 9 Rules Rela tive to the Circle This table shows conversions from degrees Fahrenheit (ºF) directly to degrees Celsius (ºC) and vice versa.It covers the range of temperatures used in most hardening, tempering and annealing operations. Lower, higher and intermediate conversions can be made by substituting a known Fahrenheit (ºF) or Celsius (ºC) temperature figure in either of the following formulas: ºF ºC –160 –107 –140 –96 –120 –84 –100 –73 –80 –62 –60 –51 –40 –40 –20 –29 0 –18 20 –7 32 0 40 4 60 16 80 27 100 38 120 49 140 60 160 71 ºF ºC 180 82 200 93 212 100 220 104 300 149 400 204 500 260 600 316 700 371 800 427 1000 538 1200 649 1400 760 1600 871 1800 982 2000 1093 2200 1204 Degrees Centigrade Degrees Fahrenheit High Temperatures Judged by Color 400 752 Red heat, visible in the dark 525 975 Red heat, visible in daylight 700 1292 Dark red 900 1652 Cherry-red 1100 2012 Orange-red 1300 2372 Yellow-white 1500 2732 Brilliant white Degrees Centigrade Degrees Fahrenheit Colors for Tempering 221.1 430 Very pale yellow 237.8 460 Straw-yellow 254.4 490 Yellow-brown 260.0 500 Brown-yellow 271.1 520 Brown-purple 282.2 540 Full purple 293.3 560 Full blue 591 starrett.com R eference T ables