Home / Topics / Measurement & Math Tools
Significant figures
Beginner
Digits that carry meaning in a measurement.
Significant figures are the digits that carry information about a measurement's precision. Non-zero digits count; zeros between digits count; leading zeros do not; trailing zeros count only if there is a decimal point or they are written in scientific notation.
0.00450 has three sig figs (4, 5, 0). 1200 may have two, three or four; writing 1.20×10³ makes it three.
Do not keep every calculator digit. The final answer cannot be more precise than the least precise input.
In more detail
Significant figures are the digits in a number that carry meaning about its precision. Leading zeros do not count, while trailing zeros in a number with a decimal point do.
Real-world uses
- A lab reading of 2.50 cm tells the reader the measurement is precise to the hundredth of a centimetre.
- Scientific journals require results to be quoted with an appropriate number of significant figures.
- A reading of 2.50 V on a voltmeter tells you the value is precise to the hundredths place, while 2.5 V suggests a coarser instrument.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
How many significant figures are in 0.0040?
Two: the 4 and the final 0. The leading zeros only locate the decimal point.
How many significant figures are in 3000?
It is ambiguous. Write 3.0 × 10 to the power 3 to show two, or 3.000 × 10 to the power 3 to show four.
Do trailing zeros count as significant?
Only if there is a decimal point or they follow a decimal point. 300 has one significant figure written plainly, but 300. has three.
Related topics in Measurement & Math Tools
Screw gauge · Measuring time · Mass vs weight · Rounding rules · Accuracy vs precision · Systematic error