3.1 Measurement & unit conversion (US/metric, F/C, mixed units)

Measurement on the Job

Measurement questions are the most common single topic on the WorkKeys Applied Math test. Nurses convert medication doses, carpenters add board lengths, warehouse clerks total package weights, and cooks scale recipes. The test gives you a calculator and a formula sheet, but it will not tell you which conversion to use. You have to read the units in the problem and line them up correctly. This section covers the US customary system, the metric system, temperature, and mixed-unit arithmetic.

The conversion facts you must know

The formula sheet lists common conversions, but working quickly means knowing the core relationships cold. Keep this reference in your head:

Converting within one system

To convert, decide whether the answer should be a bigger or smaller number, then multiply or divide.

Example - feet to inches. A roll of weather stripping is 8 feet long. How many inches is that? A foot is larger than an inch, so the number of inches will be larger: 8 ft x 12 in/ft = 96 inches.

Example - ounces to pounds. A carton of parts weighs 200 ounces. Because a pound is heavier than an ounce, the pound count is smaller: 200 oz / 16 oz/lb = 12.5 pounds.

The trick that prevents mistakes is unit cancellation. Write the conversion as a fraction so the unit you are leaving cancels: 200 oz x (1 lb / 16 oz) = 12.5 lb. The 'oz' on top and bottom cancel, leaving pounds.

Converting between US and metric

Cross-system conversions use the bridge facts at the bottom of the table.

Example - miles to kilometers. A delivery route is 45 miles. At about 1.61 km per mile: 45 mi x 1.61 km/mi = 72.45 km.

Example - kilograms to pounds. A metric shipment lists 30 kg. Using 1 kg = 2.2 lb: 30 kg x 2.2 lb/kg = 66 pounds.

Example - liters to gallons. A tank holds 50 liters. Since 1 gallon = 3.79 L, divide: 50 L / 3.79 L/gal = 13.2 gallons.

Temperature conversion

Temperature is the one conversion that uses a formula rather than a simple multiplier, because the two scales do not start at the same zero. Memorize both directions:

• Celsius to Fahrenheit: F = (9/5 x C) + 32
• Fahrenheit to Celsius: C = 5/9 x (F - 32)

Example - Celsius to Fahrenheit. A commercial oven is set to 180C. Convert: F = (9/5 x 180) + 32 = 324 + 32 = 356F.

Example - Fahrenheit to Celsius. A walk-in freezer reads 5F. Convert: C = 5/9 x (5 - 32) = 5/9 x (-27) = -15C.

Order of operations matters: for Celsius, subtract 32 first, then multiply by 5/9. Doing it out of order is the most common error on these items.

Mixed-unit arithmetic

Workplace measurements often come in two units at once - feet and inches, hours and minutes, pounds and ounces. The safe method is to convert everything to the smaller unit, do the math, then convert back.

Example - adding lengths. A cabinet run is built from three sections, each 7 ft 9 in wide. What is the total width? Convert each to inches: 7 ft 9 in = (7 x 12) + 9 = 93 in. Three sections: 93 x 3 = 279 in. Convert back: 279 / 12 = 23 with remainder 3, so 23 ft 3 in.

Example - adding times. A machine completes three production batches, each taking 1 hour 50 minutes. Total run time? Convert to minutes: 1 h 50 min = 110 min. Three batches: 110 x 3 = 330 min. Convert back: 330 / 60 = 5 with remainder 30, so 5 hours 30 minutes.

Example - subtracting mixed units. A shipment should weigh 12 lb, but the scale reads 10 lb 6 oz. How much is missing? Convert both to ounces: 12 lb = 192 oz; 10 lb 6 oz = 166 oz. Difference: 192 - 166 = 26 oz = 1 lb 10 oz.

Rounding sensibly

Cross-system factors like 2.2 lb/kg and 1.61 km/mi are approximations, so answers will be close but not exact. Round to a sensible precision for the context and match the rounding the answer choices imply.

The habit that earns points

Always write the unit next to every number, and let the calculator handle the arithmetic while you focus on choosing the right conversion factor. Estimate first: 356F for a 180C oven feels right, while 148F would signal a formula slip that a common-sense check catches before you bubble it in.