Count or round significant figures. This free sig fig calculator counts the significant figures in any number (with correct trailing-zero and decimal rules) and rounds to a chosen number of sig figs.
Your number
sig figs
Type the number exactly as written — trailing zeros and the decimal point matter. For example “120” has 2 significant figures, but “120.” has 3 and “120.0” has 4.
Significant figures
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Enter a number
Decimal places
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Rounded to N
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Scientific notation
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Rules used: all non-zero digits count; zeros between significant digits count; leading zeros don’t; trailing zeros count only when a decimal point is present.
Use this free significant figures calculator to count the significant figures in a number, or round it to a chosen number of sig figs. Type the number exactly as written — trailing zeros and the decimal point matter.
What this significant figures calculator does
A significant figures calculator counts how many digits in a number actually carry meaning (its sig figs), and can round a number to a set number of them. It applies the standard rules for zeros automatically.
The rules for significant figures
Rule
Example
All non-zero digits count
3.14 → 3 sig figs
Zeros between digits count
1002 → 4 sig figs
Leading zeros don’t count
0.0042 → 2 sig figs
Trailing zeros count only with a decimal point
120 → 2, but 120. → 3
Why trailing zeros are tricky
In “120” the trailing zero is ambiguous, so it’s treated as not significant (2 sig figs). Writing “120.” or “120.0” makes the zeros significant (3 and 4 sig figs). That’s why this calculator uses the number exactly as you type it.
Rounding to significant figures
To round 0.004520 to 2 sig figs, keep the first two significant digits: 0.0045. Enter a value in the “round to” field and the calculator does it, including the scientific-notation form.
How to use the significant figures calculator
Type your number exactly as written.
Read the significant-figure count.
Optionally enter a number to round to that many sig figs.
Significant Figures FAQ
How do I count significant figures?
Count all non-zero digits, any zeros between them, and trailing zeros when a decimal point is present. Leading zeros never count. So 0.00120 has 3 sig figs.
Do trailing zeros count?
Only when there's a decimal point. "120" has 2 significant figures, but "120." has 3 and "120.0" has 4. Type the number exactly as written.
How do I round to significant figures?
Keep the required number of significant digits and round the rest. 0.004520 to 2 sig figs is 0.0045. Enter the number in the "round to" field.
Why don't leading zeros count?
They only set the decimal position and carry no measured information. In 0.0042, the two leading zeros aren't significant, so it has 2 sig figs.
What about numbers in scientific notation?
The significant figures are those in the mantissa. For 6.022 × 10²³ there are 4 significant figures. The calculator reads this format too.
Is the significant figures calculator free?
Yes, this significant figures calculator is completely free, needs no sign-up, and gives instant results in your browser.
