What are significant figures?
Significant figures are the digits in a measured value that communicate precision. Non-zero digits count, zeros between non-zero digits count, and trailing zeros count when a decimal point makes the precision explicit.
Free chemistry and physics helper
Significant Figures Calculator
Count, round, and calculate sig figs with step-by-step explanations and lab-report-ready answers.
Step-by-step explanation
Step 1
Find the first non-zero digit. Leading zeros before that digit are not significant.
Step 2
Count the significant digits: 4, 5, 0.
Step 3
0.00450 has 3 significant figures.
Lab Report Answer
0.00450 has 3 significant figures based on the written digits and zero rules.
Rules for counting significant figures
Leading zeros are placeholders, not significant figures. Captive zeros between non-zero digits are significant. Trailing zeros after a decimal point are significant. Whole-number trailing zeros without a decimal point are ambiguous.
How to round to significant figures
Start at the first non-zero digit, keep the requested number of significant digits, then check the next digit. If the next digit is 5 or greater, round up.
Round a number to 2, 3, or 4 significant figuresAddition and subtraction rule
For addition and subtraction, the final answer is rounded to the least precise decimal place. The number of significant figures in each input is not the deciding rule for this operation type.
Multiplication and division rule
For multiplication and division, the final answer is rounded to the fewest significant figures in the measured inputs.
Scientific notation and sig figs
Scientific notation separates the measured digits from the power of ten. The coefficient determines the significant figures; the exponent only changes the size of the value.
How to use this significant figures calculator
The calculator is built for learning, checking work, chemistry and physics labs, and quick precision decisions. It keeps the calculation and the rule explanation together so you can see why the answer should be reported a certain way.
Enter the measured value or expression
Use a single value such as 0.00450, an ambiguous value such as 100, scientific notation such as 3.76e4, or a simple arithmetic expression.
Choose the significant-figures task
Count significant figures, round to a target count, calculate with addition or multiplication rules, or convert a value to scientific notation.
Use the explanation, not only the number
The result includes the final answer, the rule used, warnings for ambiguous zeros, step-by-step reasoning, and a short lab-report-ready sentence.
Common confusing examples
0.00450
3 significant figures: 4, 5, and the final decimal zero.
Read the answer
100
Ambiguous unless written as 100., 1.0 x 10^2, or 1.00 x 10^2.
Read the answer
12.5 + 0.003
Report 12.5 because the least precise decimal place is tenths.
Reference sources
This calculator is written as a study helper, not as a replacement for a lab manual. The rule explanations are checked against standard chemistry and measurement references.
OpenStax Chemistry 2e: Measurement Uncertainty, Accuracy, and Precision
Textbook context for measured quantities, exact values, and significant figures.
NIST: Basic definitions of uncertainty
Measurement uncertainty background from the National Institute of Standards and Technology.
Chemistry LibreTexts: Significant Digits
Additional chemistry-oriented explanation of significant digits and precision.
Significant figures FAQ
A significant figures calculator counts, rounds, or calculates values using significant figure rules so the reported answer matches the precision of the measurements.
0.00450 has 3 significant figures. The leading zeros are not significant, while 4, 5, and the trailing zero after the decimal point are significant.
100 is ambiguous when written without a decimal point. It may have 1, 2, or 3 significant figures depending on the measurement context.
For addition and subtraction, round the final result to the least precise decimal place among the measured values.
For multiplication and division, round the final result to the fewest significant figures among the measured values.
No. In scientific notation, the coefficient shows the significant figures. The exponent changes the size of the number, not the precision count.
Exact counted values and defined constants usually do not limit significant figures. Measured values control the reported precision.
Usually no. Keep extra digits during intermediate work, then round the final answer using the correct significant-figures or decimal-place rule.
Continue with the right next step
Round to significant figuresRound a number to 2, 3, or 4 significant figures with worked steps.Significant figures rulesReview zero rules, arithmetic rules, rounding, and scientific notation.Interactive sig fig practiceGenerate fresh counting, rounding, notation, and arithmetic problems.Why 0.00450 has 3 sig figsSee which leading and trailing zeros count in 0.00450.How many sig figs are in 100?Learn why whole-number trailing zeros need clearer notation.