Significant figures are the digits in a number that reliably indicate the true value.
For example, if using a scale reliable to the nearest gram, digits beyond the gram are insignificant. If using a ruler with ticks every 1 centimeter, then the ruler is certain to 1 centimeter but reliable to one decimal despite some uncertainty.
Lastly, exact numbers ("3 people" or "1/2" in "1/2mv^2) don't have significant figures, though some may consider them to have infinite significant figures for calculation purposes.
"100" has 1 significant figure because trailing zeros are insignificant by default. If written "100" (with an underline on digit 2), it would have 2 significant figures. rule 5
"100." has 3 significant figures because zeros up to the decimal are significant. rule 3
"100.00" has 5 significant figures because zeros after the decimal are significant. rule 4
We count significant figures using the following rules:
We have a calculator on our homepage to help you with your significant figure calculations.Written by Quentin Truong.