How to round a number off to 1 significant figure (1sf or 1 sig fig)

Rounding to 1 significant figure is very useful when you need to estimate. Your 1^st significant figure is the first number from the start of the number you need to round (ignoring any zeros at the start). Let’s take a look at a few examples:

Example 1:

Round 574.89 to 1 significant figure

First highlight your first significant figure:

574.89

Now since the number after 5 is 7 (which is 5 or above) you round the number up to 600.

Example 2:

Round 4193 to 1 significant figure.

Again, highlight your first significant figure.

4193

Now since the number after 4 is 1 (which is less than 5) you round the number down to 4000.

Example 3:

Round 31.586 to 1 significant figure.

Again, highlight your first significant figure.

31.586

Now since the number after 3 is 1 (which is less than 5) you round the number down to 30.

Example 4:

Round 6.497 to 1 significant figure.

Again, highlight your first significant figure.

6.497

Now since the number after 6 is 4 (which is less than 5) you round the number down to 6.

Example 5:

Round 394178.314 to 1 significant figure.

Again, highlight your first significant figure.

394178.314

Now since the number after 3 is 9 (which is 5 or above) you round the number up to 400000.

Example 6:

Round 0.003814 to 1 significant figure.

Again, highlight your first significant figure. Since the number is a small number, you ignore the zeros at the start of the number.

0.003814

Now since the number after 3 is 8 (which is 5 or above) you round the number up to 0.004 (don’t put 0’s after 0.003)

Example 7:

Estimate this calculation by rounding the numbers off to 1 significant figure.

482 × 12.781

Again all you need to do is round the number off to 1 significant figure.

482 = 500

12.781 = 10

So 500 × 10 is about 5000.