SigFigs

Significant Figures Calculator

Precision-controlled rounding.

Number

Significant figures

Rounded to sig figs

12,300

What you entered

Number: 12345.6789Significant figures: 3

1
Determine the decimal position to round at
3 sig figs at magnitude 10^5= round at 10^2
2
Round to that position
round(12345.6789)= 12300

Result

Rounded to sig figs: 12,300

12345.6789 rounded to 3 significant figures is 12300.

Numbers rounded to significant figures

Significant figures count meaningful digits from the first non-zero one, which is different from counting decimal places.

Number	Significant figures	Result
3.14159265	3	3.14
3.14159265	5	3.1416
0.0012345	3	0.00123
0.005678	2	0.0057
123456	3	123000
98765	2	99000

The leading zeros in 0.0012345 are not significant - they only place the decimal point - so three significant figures gives 0.00123, which is five decimal places. That is the distinction the whole concept rests on. Rounding to significant figures preserves relative precision across very different magnitudes, which is why scientific work uses it rather than decimal places. In a calculation, the result should carry no more significant figures than the least precise input: multiplying a value known to 3 significant figures by one known to 5 gives an answer good to 3.

Precision, not just decimal places

Significant figures count all the meaningfully precise digits in a number, starting from the first non-zero digit — 12300 to 3 sig figs is 12300 (with the 300 approximate), while 0.0123 to 3 sig figs keeps all three non-zero digits shown.

Why scientists care about this

Reporting a measurement with more significant figures than your instrument can actually justify implies false precision — sig figs are how scientific results communicate their real level of confidence.

Frequently asked questions

How many significant figures does 0.00320 have?

Three. Leading zeros (0.00) are never significant — they just locate the decimal point. The digits 3, 2, and the trailing 0 are all significant because that trailing zero indicates measured precision.

What's the difference between significant figures and decimal places?

Decimal places count digits after the decimal point regardless of leading zeros. Significant figures count all meaningful digits from the first non-zero digit onward. For 0.00320: 5 decimal places, but only 3 significant figures. Use sig figs for measurement precision; decimal places for fixed-format rounding.

Why is the trailing zero in 2.50 significant but the zeros in 2500 are ambiguous?

Writing 2.50 instead of 2.5 signals that you measured to the hundredths place — the zero carries information. In 2500, it's unclear whether the zeros are measured or just placeholders. Scientific notation resolves this: 2.500 × 10³ = 4 sig figs; 2.5 × 10³ = 2 sig figs.

How do sig figs work in multiplication vs. addition?

In multiplication and division, round the result to match the input with the fewest significant figures. In addition and subtraction, round to match the input with the fewest decimal places. Different rules because the operations propagate uncertainty differently.

My teacher marked me wrong for reporting 12.345678 from a calculator — why?

A calculator gives as many digits as it can, but your inputs likely had far fewer significant figures. If your measured values had 3 sig figs, your answer should too — reporting 12.3, not 12.345678. Extra digits imply a precision your measurements don't support.