Color coded digits
Each digit is marked as significant, not significant or ambiguous, with a plain English reason underneath. You learn the rule while you get the answer.
Significant Figures Calculator
Count sig figs, round any number to the precision you need, and solve full calculations under the correct significant figures rules. Every digit is color coded so you can see exactly which ones count, and every answer comes with the reasoning written out.
Digit by digit breakdownRounding plus scientific notationAdd, subtract, multiply, divideNo sign up, no ads in the tool
Significant figures calculator tool
Decimals, whole numbers, negatives and scientific notation such as 3.20e4 are all accepted.
Optional. The rounded version is shown alongside the count.
Use + for add, - for subtract, * or x for multiply, / for divide. Steps run left to right, which matches how sig fig homework is normally marked.
Why this significant figures calculator is different
Most sig fig tools hand back a single number and leave you guessing. This one shows the working, so it doubles as a study aid rather than just an answer machine.
Three tools in one panel
Counting, rounding and full calculations share the same interface, so you never have to hunt for a second page when a question changes shape.
Ambiguous zeros handled properly
Trailing zeros in a whole number such as 1200 are genuinely ambiguous. A single toggle switches between both accepted conventions instead of pretending one exists.
Step by step arithmetic
Chained calculations show every step, the rule that governs it, and the precision that survives, which is exactly what lab reports and exam mark schemes ask for.
Scientific notation built in
Every result is also given in scientific and E notation, the only unambiguous way to write a value with a fixed number of significant figures.
Instant and private
The whole calculator runs in your browser with no libraries to download. Results update as you type and nothing you enter is ever sent anywhere.
How to use the sig fig calculator
Pick the mode that matches your question, type your value, and read the answer with its explanation.
Choose your mode
Count sig figs tells you how many a number has. Round to sig figs trims a number to a set precision. Calculate with sig figs solves an expression and rounds the answer correctly.
Type the number or expression
Decimals, negatives and scientific notation such as 6.02e23 all work. Results refresh as you type, so there is no submit button to hunt for.
Check the digit map
Teal digits are significant, faded digits are not, and amber digits are ambiguous trailing zeros. The notes below the map name the rule behind each decision.
Copy the answer you need
Take the plain result, the scientific notation form or the rounding table, then paste it straight into your homework, lab report or spreadsheet.
Significant figures rules, in one table
These five rules decide every count the calculator makes. Read them once and most sig fig questions stop being guesswork.
| Rule | What it says | Example | Sig figs |
|---|---|---|---|
| Non zero digits | Every digit from 1 to 9 is always significant. | 3852 | 4 |
| Captive zeros | Zeros sitting between two non zero digits always count. | 90.05 | 4 |
| Leading zeros | Zeros before the first non zero digit never count. They only place the decimal point. | 0.00407 | 3 |
| Trailing zeros with a decimal | Zeros after the last non zero digit count when a decimal point is present. | 0.004070 | 4 |
| Trailing zeros without a decimal | Ambiguous by default and usually treated as not significant unless the source says otherwise. | 1200 | 2 or 4 |
| Exact numbers | Counted items and defined conversions have unlimited significant figures and never limit a result. | 12 eggs | Unlimited |
Who this calculator helps
Significant figures show up far beyond chemistry class, and the tool is built for all of it.
Chemistry and physics students
Molar masses, titration volumes and kinematics answers all get marked on precision, not just the digits.
Lab technicians and researchers
Report measured values at the precision your instrument actually delivers instead of the precision your calculator invented.
Engineers and drafters
Keep tolerances honest when converting units or scaling dimensions across a drawing set.
Teachers and tutors
Project the digit map on screen and the leading zero question answers itself in about five seconds.
Data and finance analysts
Round consistently before publishing so a spreadsheet does not imply nine digits of accuracy it never had.
Anyone checking homework
Confirm a sig fig answer in seconds, with the reasoning visible so you can spot where the working went wrong.
Significant figures FAQ
The questions students and lab users ask most about sig figs, answered without the textbook fog.
How many significant figures does 0.00250 have?
Three. The three leading zeros only position the decimal point, so they do not count. The 2 and the 5 are non zero digits and always count, and the final zero counts because it is a trailing zero after a decimal point. Writing it as 2.50 times 10 to the power of minus 3 makes the three significant digits obvious.
Are trailing zeros significant in a number like 1200?
It depends on the convention your course uses, which is why the calculator offers a toggle. Without a decimal point the trailing zeros are ambiguous and most textbooks treat 1200 as two significant figures. If the value really was measured to four, write it as 1200. with a trailing decimal point, or as 1.200 times 10 to the power of 3, and the ambiguity disappears.
What is the rule for significant figures when multiplying and dividing?
The answer keeps the same number of significant figures as the input with the fewest. For example 4.56 multiplied by 1.4 gives 6.384 on a calculator, but 1.4 only carries two significant figures, so the reported answer is 6.4. Count sig figs for multiplication and division, and count decimal places for addition and subtraction.
How do significant figures work for addition and subtraction?
Precision is governed by decimal places rather than by significant figures. The answer is rounded to the fewest decimal places among the values you added. So 13.25 plus 8.1 gives 21.35 exactly, but 8.1 has only one decimal place, so the answer is reported as 21.4 rather than 21.35.
How do I round 3.14159 to 3 significant figures?
Count three digits from the first non zero digit, which gives 3.14, then look at the next digit to decide the rounding. The following digit is 1, which is below 5, so the third digit stays as it is and the answer is 3.14. Had the next digit been 5 or more, the third digit would have been rounded up to give 3.15.
Do exact numbers and constants limit significant figures?
No. Counted quantities such as 12 flasks and defined conversions such as 1 inch equalling exactly 2.54 centimetres carry unlimited significant figures, so they never restrict a result. Only measured values, which always carry uncertainty, set the precision of your final answer.
Should I round at every step of a multi step calculation?
No. Carry the full precision through the intermediate steps and round only once at the end, because rounding early stacks small errors into a visibly wrong final answer. The calculator follows this approach, showing you the governing rule at each step while it keeps the unrounded value until the last line.
What is the difference between significant figures and decimal places?
Decimal places count digits after the decimal point, while significant figures count meaningful digits starting from the first non zero digit anywhere in the number. The value 0.00456 has five decimal places but only three significant figures. Rounding modes for both are built into the tool so you can switch between them without a second calculator.
Get the precision right the first time
Scroll back up, drop your number into the calculator and read the digit map. Counting, rounding and full sig fig arithmetic take about three seconds each, and the reasoning stays on screen.