The factor-label method is a method for converting between units in science. It involves writing the quantity and units to convert, equating the desired quantity to the given quantity to find the appropriate conversion factors, and then multiplying the given quantity by the conversion factors to eliminate the unwanted units and leave only the desired units. For example, to convert 12 km to meters, we write 12 km, use the conversion factor that 1 km = 1000 m, and calculate 12 km * (1 km/1000 m) = 12,000 m. To convert 72 km/h to m/s, we write 72 km/h, use the conversion factors that 1 km = 1000 m and 1 h = 3600 s, and calculate 72

1. COLEGIO INTERNACIONAL SEK - EL CASTILLO
DEPARTAMENTO DE CIENCIAS NATURALES
Natural Sciences
Unit conversion using the Factor-label method
The factor-label method is a method to convert units in science. To convert units we
need what we call a conversion factor. Conversion factors are valid relations between
units of the same kind or equities expressed as a fraction.
For example: kilometres and metres are both units of distance. We know that 1
kilometre equals 1000 metres. Therefore the conversion factor would be (or
).
We can use this conversion factors in a simple method to convert both simple ( for
example : km to m) or complex units (km/h to m/s).
When converting units with the Factor- label method follow these steps.
1. Write down the quantity and the units you want to convert.
In our first example we are going to convert metres to kilometers.
Example a Example b
12 km (km m) 72 ( km/h m/s or  )
2. Equate the desired quantity to the given quantity
Example a Example b (in this case we are really
1km= 1000m converting two units km and hours)
1km= 1000m
1h = 3600 s
3. Find the conversion factor you can use. You will need as many conversion
factors as units you need to convert.
Example a Example b
4. Multiply given quantity by the appropriate conversion factors to eliminate
units you don’t want and leave units you do want.
Write the conversion factor so that the units given cancel and the units
desired are left.

2. Example a Example b (since we want to convert
12 km · two units, we need to multiply by two
conversion factors)
72 ·
5. Cancel out the units and complete the math.
Example a Example b (since we want to convert
12 km · = two units, we need to multiply by two
conversion factors)
12 · = 12 000 m
72 · =
72 · =
72 · = =
20