**To find circumference** – multiply the diameter by 3.1416; or, divide diameter by 0.3183.

**To find diameter** – multiply the circumference by 0.3183; or, divide circumference by 3.1416.

**To find radius** – multiply the circumference by 0.15915; or, divide circumference by 6.28318;

or, divide diameter by 2.

**To find the side of a square to be inscribed in a circle** – multiply diameter by 0.7071; or,

multiply the circumference by 0.2251; or, divide the circumference by 4.4428.

**T****o find the side of a square to equal the area of a circle** – multiply the diameter by 0.8862;

or, divide diameter by 1,1284; or, multiply the circumference by 0.2821; or, divide circumference

by 3.545.

**To find the area of a circle** – multiply the circumference by one-quarter of the diameter; or,

multiply the square of the diameter by 0.7854; or, multiply the square of the circumference by

0.7958; or, multiply the square of one-half the diameter by 3.1416.

Doubling the diameter of a circle increases the area 4 times.

A side multiplied by 1.412 = the diameter of a circle which will circumscribe the given square.

A side multiplied by 4.443 = the circumference of its circumscribing circle.

A side multiplied by 1.1284 = the diameter of a circle equal in area to that given square.

A side multiplied by 3.545 = circumference of an equal circle.

**To find diagonal of a square** – multiply side by 1.4142.

**To find the area of an ellipse** – multiply the product of its axes by 0.7854; or, multiply the product of its semi-axes by 3.14159.

**Contents of a cylinder** = area of end X length.

**Contents of a wedge** = area of triangular base X altitude.

**Surface of a cylinder** = length X circumference plus area of both ends.

**Surface of a sphere** = diameter squared X 3.1416; or, diameter X circumference.

**Contents of a sphere** = diameter cubed X 0.5236.

**Contents of a pyramid or cone, right or oblique, regular or irregular** = area of base X one-third of the altitude.

**Area of a triangle** = base X one-half the altitude.

**Area of parallelogram** = base X altitude.

**Area of trapezoid** = altitude X one-half the sum of parallel sides.

**To find distance across the corners of hexagons** – multiply the distance across the flats by 1.1547.

1 gal. water = 8.3 lb.

1 hp = 745.2 watts.

1 BTU = .252 kg calories = 0.2930 watt hours.

1 BTU per lb. = 1.8 cal per gram.

1 kw-hr = 3412 BTU per hour.

1 kw-hr will evaporate 3.5 lb of water at 212°F.

1 kw-hr will raise 22.75 lb of water from 62°F to 212°F.

1 gal. = 231 cu.in. = 3.785 liters = .1337 cu.ft.

1 cu.ft. = 1728 cu.in. = .03704 cu.yd. = 7.481 gal.

To find the equivalent, in terms of a unit in the customary system, of a given number of metric units, multiply or divide their number (as indicated) by the factor shown.

Thus: 10 millimeters are equivalent to 10 x 0.03937 inches or to 10 ÷ 25.4 inches.

Millimeters x .03937 = inches; or ÷ 25.4 = inches.

Centimeters x .03937 = inches; or ÷ 25.4 = inches.

Meters x 39.37 = inches.

Meters x 3.28 = feet.

Kilometers x 3280.8 = feet.

Square meters x 10.764 = square feet.

Cubic centimeters ÷ 16.387 = cubic inches.

Cubic centimeters ÷ 3.70 = fluid drams (U.S.P.).

Cubic centimeters ÷ 29.57 = fluid ounces (U.S.P.).

Cubic centimeters ÷ 3.531 x 10 *-5* = cubic feet.

Cubic meters x 35.314 = cubic feet.

Liters x 61.025 = cubic inches.

Liters x 33.81 = fluid ounces (U.S.P.).

Liters x .2642 = gallons (231 cubic inches).

Liters ÷ 3.785 = gallons (231 cubic inches).

Liters ÷ 28.317 = cubic feet.

Grams x 15.432 = grains.

Grams (water) ÷ 29.57 = fluid ounces.

Grams ÷ 28.35 = ounces avoirdupois.

Grams per cubic centimeter ÷ 27.7 = pounds per cubic inch.

Kilograms x 2.2046 = pounds.

Kilograms x 35.3 = ounces avoirdupois.

Kilograms per square centimeter x 14.223 = pounds per square inch.

Kilo per meter x .672 = pounds per foot.

Kilo per cubic meter x .062 = pounds per cubic foot.

Kilowatts x 1.34 = h.p. (33,000 foot pounds per minute).

Watts ÷ 746 = horse power.

Centigrade x 1.8 + 32 = degrees Fahrenheit.