Imperial units of length

The imperial system is still common in the United States and the United Kingdom. It uses different conversion factors than the metric system — they are not all powers of ten.

The four common units

The conversion factors

• $1\text{ft}=12\text{in}$
• $1\text{yd}=3\text{ft}=36\text{in}$
• $1\text{mi}=1760\text{yd}=5280\text{ft}=63360\text{in}$

Unlike the metric system, the steps are not all the same. You really do have to remember three different numbers: 12, 3 and 1760.

How to convert

The rule is the same as in the metric system:

• Smaller → larger : divide.
• Larger → smaller : multiply.

Examples

1. $5\text{ft}=?\text{in}$ — multiply by 12: $5\times 12=60\text{in}$.
2. $36\text{ft}=?\text{yd}$ — divide by 3: $36/3=12\text{yd}$.
3. $2\text{mi}=?\text{ft}$ — multiply by 5 280: $2\times 5280=10560\text{ft}$.
4. $3520\text{yd}=?\text{mi}$ — divide by 1 760: $3520/1760=2\text{mi}$.

A useful comparison with the metric system

A quick rule of thumb (these are not exact, but handy for everyday estimating):

• $1\text{in}\approx 2.5\text{cm}$
• $1\text{ft}\approx 30\text{cm}$
• $1\text{yd}\approx 1\text{m}$ (a metre is slightly longer)
• $1\text{mi}\approx 1.6\text{km}$

Read more

• Length unit conversions – guide
• Metric system

Practise

• Imperial – smaller to larger
• Imperial – larger to smaller
• Compare imperial units