Significant Figures Calculator
The significant figures calculator counts the sig figs in any number, rounds a value to the precision you choose, and runs arithmetic that applies the correct sig fig rules automatically. It is built for students and anyone working in chemistry, physics, or engineering who needs answers reported to the right precision.
Significant figures are the digits that carry real information about how precise a measurement is. Writing 12.5 cm implies precision to the nearest 0.1 cm, while 12.50 cm claims the nearest 0.01 cm. This tool makes those rules visible: it highlights which digits count, names the rule behind each result, and rounds in both decimal and scientific notation.
How to Use the Significant Figures Calculator
The tool has three tabs — Count, Round, and Calculate — selected from the buttons at the top. Pick the one that matches your task.
Count significant figures
On the Count tab, type a number — decimals and scientific notation like 1.23e-4 are accepted — then press Enter or the Count button. Each digit is color-coded green (significant) or gray (not significant), with the total count and the rules that applied.
Round to a precision
On the Round tab, enter your number, then choose how many sig figs to keep — tap a quick button from 1 to 6 or type any value up to 15. Press Round to see the result in both decimal and scientific notation.
Calculate with sig fig rules
On the Calculate tab, enter the first number, pick an operation (+, −, ×, ÷), and enter the second number. The result applies the correct sig fig rule for that operation and shows a step-by-step breakdown.
Read the explanation
Every result names the rules behind it, so you learn why each digit counts. Add a decimal point to mark trailing zeros as significant (write 100. instead of 100) and check your own work against the highlighted digits.
Features
Visual Digit Highlighting
When counting, each digit is color-coded — green for significant, gray for not — so you can see the rules at a glance and verify your own counting.
Rule Explanations
The calculator names which rules applied — leading zeros, trailing zeros, or sandwiched zeros — so you see exactly why each digit was counted.
Dual Output Formats
Rounded results appear in both standard decimal and scientific notation — handy for the very large or very small numbers common in chemistry and physics.
Arithmetic with Proper Rules
Addition and subtraction round to the fewest decimal places; multiplication and division round to the fewest significant figures — applied automatically.
Step-by-Step Breakdown
For calculations, see the sig figs or decimal places in each input, the rule that applies, the raw result, and the properly rounded final answer.
Scientific Notation Support
Enter numbers like 6.022e23 or 1.5e-10 in any tab — the calculator parses, counts, and rounds them correctly.
Flexible Precision
Round with one-tap buttons for 1 to 6 sig figs, or type any custom value up to 15 for high-precision work.
Private & Browser-Based
All calculations happen locally in your browser. No data is sent to any server, and nothing is stored or tracked.
Frequently Asked Questions
How do I count significant figures?
All non-zero digits count, zeros between non-zero digits count, leading zeros never count, and trailing zeros after a decimal point count. On the Count tab, type your number and the calculator highlights each digit and shows the total automatically.
How many significant figures does 100 have?
The number 100 written without a decimal point has only 1 significant figure — the trailing zeros are ambiguous. To indicate all three digits are significant, write it as 100. with a decimal point, or as 1.00 × 10².
Are leading zeros ever significant?
No. Leading zeros are only placeholders that show where the decimal point sits. For example, 0.0045 has 2 significant figures — just the 4 and the 5. The zeros before the 4 are never counted.
Why do trailing zeros after a decimal count?
They indicate precision. Writing 1.50 instead of 1.5 tells the reader you measured to the hundredths place, so that extra zero is meaningful information and counts as significant.
What is the rule for addition versus multiplication?
For addition and subtraction, round the answer to match the number with the fewest decimal places. For multiplication and division, round to match the number with the fewest significant figures. The Calculate tab applies the right rule for each operation automatically.
How do I round a number to 3 significant figures?
On the Round tab, enter the number, tap the 3 quick button (or type 3 in the custom field), and press Round. The result appears in both decimal and scientific notation, along with the original number's own sig fig count.
Does scientific notation change the sig fig count?
No. Scientific notation is just another way to write the same value. 4.50 × 10³ has 3 significant figures — the same as 4500. written with a decimal point.
What about exact numbers?
Exact numbers — like counting 12 eggs or the conversion 1 km = 1000 m — have infinite significant figures and never limit your answer's precision. This calculator treats every input as a measured value, so enter exact numbers with enough sig figs that they will not be the limiting factor.
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