Find the first significant digit
Skip leading zeros, then start counting at the first non-zero digit.
Rounding calculator
Round to Significant Figures Calculator
Enter a number and choose how many significant figures to keep. The calculator shows the rounded result, the rule used, and a lab-report-ready explanation.
Step-by-step explanation
Step 1
Start counting significant figures at the first non-zero digit.
Step 2
Keep 3 significant figures and check the next digit.
Step 3
Round 12.57 to 12.6.
Lab Report Answer
12.57 rounded to 3 significant figures should be reported as 12.6.
How this rounding calculator works
Rounding to significant figures is different from rounding to decimal places. Significant figures count measured digits, starting with the first non-zero digit.
Keep the target count
Keep as many significant digits as the problem asks for, such as 2, 3, or 4 sig figs.
Check the next digit
If the next digit is 5 or greater, round up. Otherwise, leave the last kept digit unchanged.
Step-by-step rounding workflow
Ignore leading zeros
Leading zeros only place the decimal point. In 0.00450, counting starts at 4, not at the zeros before it.
Count the requested digits
If the target is 3 significant figures, keep the first three significant digits and mark the next digit as the rounding digit.
Round and preserve precision
Round up when the next digit is 5 or greater. Keep meaningful trailing zeros when they are needed to show the requested precision.
Rounding examples
12.57 to 3 sig figs
12.6
Keep 1, 2, and 5; the next digit is 7, so round up.
0.00450 to 2 sig figs
0.0045
Leading zeros do not count. Keep 4 and 5.
3.76e4 to 2 sig figs
3.8 x 10^4
Round the coefficient from 3.76 to 3.8.
100 to 2 sig figs
1.0 x 10^2
Scientific notation keeps the two significant figures visible.
98765 to 3 sig figs
98800 or 9.88 x 10^4
Use scientific notation when plain trailing zeros could hide precision.
0.09995 to 3 sig figs
0.100
The rounded answer needs trailing zeros after the decimal point to show 3 sig figs.
Common rounding mistakes
Dropping required trailing zeros
0.100 has 3 significant figures. Writing 0.1 would change the reported precision.
Rounding by decimal places instead
Rounding to 3 significant figures is not always the same as rounding to 3 decimal places.
Making whole-number zeros unclear
For values like 100 rounded to 2 or 3 significant figures, scientific notation is often clearer than plain whole-number notation.
Common rounding questions
How do you round to significant figures?
Start counting at the first non-zero digit, keep the requested number of significant digits, then use the next digit to decide whether to round up.
Do leading zeros count when rounding?
No. Leading zeros only locate the decimal point. In 0.00450, the first significant digit is 4.
Should I round intermediate steps?
For most lab work, keep extra digits during intermediate calculations and round the final answer using the required significant figures or decimal-place rule.
Why does 0.100 have 3 significant figures?
The trailing zeros are after the decimal point, so they show measured precision. Removing them changes the significant-figures count.
How should I round 100 to 2 significant figures?
Use 1.0 x 10^2 when you need the two significant figures to be unambiguous.
Can I use this for lab reports?
Yes. The calculator gives a rounded value plus a short explanation, but you should still follow any specific rounding convention from your instructor or lab manual.