Significant Figures Calculator
3
Significant Figures Count4
Rounded Value1230
Significant figures are the digits in a measurement that carry real meaning about its precision. This calculator counts the significant figures already present in a number and rounds that number to a target count of sig figs, which is essential for reporting results correctly in chemistry, physics, and engineering.
Formula
rounded = round(value × 10^(s − m)) / 10^(s − m), where m = floor(log10(|value|)) + 1
- value
- The number being rounded
- s
- Target number of significant figures (must be at least 1)
- m
- Magnitude: the number of digits before the implied decimal in |value|
How it works
- Enter a number (it may include a decimal point and a leading minus sign) and the target number of significant figures you want to keep.
- To count, the calculator strips any leading sign and leading zeros; for numbers with a decimal point every remaining digit (including trailing zeros) counts, while for whole numbers without a decimal point trailing zeros are treated as not significant.
- To round, it scales by a power of ten based on the number’s magnitude and the target count, rounds, and scales back so only the requested number of meaningful digits remain.
Worked examples
Count the significant figures in 0.0250.
- Drop the leading zeros: 0.0250 becomes the digits 250 after the decimal.
- Because the number has a decimal point, the trailing zero counts.
- Three written digits plus the trailing zero give four significant figures.
0.0250 has 4 significant figures
Round 3.14159 to 3 significant figures.
- Magnitude m = floor(log10(3.14159)) + 1 = 1.
- Scale by 10^(3 − 1) = 100: 3.14159 × 100 = 314.159, round to 314.
- Scale back: 314 / 100 = 3.14.
3.14159 to 3 sig figs = 3.14
Frequently asked questions
- Are trailing zeros significant?
- It depends on the decimal point. In 0.0250 or 45.60 the trailing zero is significant because the decimal point shows it was measured. In a whole number like 4560 with no decimal point, trailing zeros are ambiguous, so this calculator does not count them — 4560 reads as three significant figures.
- Do leading zeros count as significant figures?
- No. Leading zeros only place the decimal point and never count. That is why 0.0250 has four significant figures (2, 5, and two of the meaningful zeros are stripped) rather than five or six.
- Why does rounding to sig figs differ from rounding to decimal places?
- Rounding to decimal places keeps a fixed number of digits after the point regardless of size, while significant figures keep a fixed number of meaningful digits starting from the first nonzero one. So 0.004567 to 2 sig figs is 0.0046, but to 2 decimal places it is 0.00.
- What is the minimum target I can use?
- You must keep at least one significant figure; a target below 1 is rejected. Rounding a nonzero number to one significant figure leaves only its leading digit scaled to the right magnitude.