Ever looked at a number in science or math class and wondered, “Which digits actually matter?” That’s what significant figures (sig figs) are all about. They tell us how precise a number is. With this calculator, you simply type in a number, and it instantly shows you which digits count as significant — usually highlighted in green. It can even round your number to a set number of sig figs, so you don’t have to do the rules in your head.
What “significant figures” really mean
Significant figures are the digits in a number that carry meaning. They’re the digits you can trust.
Writing 12.3 m says you measured to the nearest tenth → 3 sig figs.
Writing 12.300 m says you went much further in precision → 5 sig figs.
In short: more sig figs = more precise measurement.
Why it’s important in real life
Science and labs: Ensures results match the measuring tool’s precision.
Engineering and design: Prevents errors when tiny differences matter.
Everyday use: Stops you from reporting fake precision, like saying your weight is “72.348 kg” when the scale only shows 72.3.
Using the right number of significant figures means your results look professional and trustworthy.
Quick rules for spotting sig figs
Here are the golden rules, explained simply:
All non-zero digits count.
Example: 123 → 3 sig figs.
Zeros in the middle count.
Example: 1002 → 4 sig figs.
Leading zeros don’t count.
Example: 0.0045 → 2 sig figs (4 and 5 only).
Trailing zeros after a decimal count.
Example: 2.300 → 4 sig figs.
Trailing zeros in whole numbers are tricky.
Example: 1500 could be 2, 3, or 4 sig figs.
To be clear, use scientific notation: 1.50 × 10³ = 3 sig figs.
Exact numbers are special.
Example: 12 eggs = exact. Infinite sig figs.
How the calculator works step by step
Enter your number — type it exactly as you see it (with decimals or in scientific notation if needed).
The calculator checks the format — is it a decimal, a whole number, or written with scientific notation?
Rules are applied — it figures out which digits count as significant and which don’t.
Highlights appear — significant digits are shown in green for clarity.
Optional rounding — you can round to 2, 3, 4, or however many sig figs you need.
Example:
Input: 0.004560
Output: digits 4, 5, 6, 0 are significant → 4 sig figs.
Common examples you’ll see
1500 → ambiguous, best written as 1.5 × 10³.
0.0200 → 3 sig figs (2, 0, 0).
3.00 × 10² → 3 sig figs.
120.0 → 4 sig figs.
Frequently Asked Questions
It’s unclear unless you add a decimal or use scientific notation.
No, they’re just placeholders.
Yes, they show measured precision.
That’s just zero, no significant figures.
Yes — treat them like any number, depending on how precise the input is.
No, unit conversions don’t add precision.
Those are exact and have unlimited sig figs.
Find the digit at your chosen place, check the next digit, and round up if it’s 5 or more. The calculator does this for you.
It removes confusion with trailing zeros and shows sig figs clearly.
For multiplication/division: match the input with the least sig figs.
For addition/subtraction: match the least precise decimal place.
