Significant figures calculator
Count how many significant figures a number has, and round it to the number of significant figures you need. Chemistry and physics students use this to report measurements with the right precision.
- Runs in your browser
- Free, no account needed
- Copy or download the result
Result
Example
0.0012300
Rounded: 1.23e-3 Input significant figures: 5 Requested significant figures: 3
How to use the significant figures calculator
- Type one number in the box, such as 0.0012300 or 4.56e7.
- Set Significant figures (1 to 100) to how many figures you want, such as 3.
- Press Run to see the rounded value, the input's significant figures and the requested count.
- Press Copy result or Download to save it.
How it works
Leading zeros never count. Zeros after a decimal point do count, so 0.0012300 has 5 significant figures.
Trailing zeros in a whole number with no decimal point are treated as placeholders, so 1200 has 2. Type 1200. with a decimal point to count all 4.
Rounding is exact and goes to the nearest value, with ties rounded away from zero. 0.0012300 to 3 figures is 1.23e-3.
The rounded value is written in e notation whenever the power of ten is not zero, so the kept zeros stay visible. 1500 to 3 figures shows as 1.50e+3.
Accepts up to 200 digits and an exponent from -1000 to 1000.
Everything runs in your browser. Your input is not uploaded or stored.
Questions and answers
How do you count significant figures?
Start at the first nonzero digit and count every digit after it. Zeros between digits always count, trailing zeros after a decimal point count, and leading zeros never count.
Do trailing zeros count as significant figures?
Only when there is a decimal point. 2.50 has 3 significant figures, but 250 has 2 under the rule this tool uses.
How many significant figures does 0.0050 have?
Two: the 5 and the zero after it. The zeros before the 5 only mark the decimal place.
Why is my answer shown in e notation?
Writing 1.50e+3 instead of 1500 shows exactly how many figures are significant. Plain 1500 would hide whether the zeros matter.