Significant Figures Calculator

Significant Figures Calculator does the two jobs that come up together: counting how many significant figures a number already has, and rounding it to a stated number of them. The counting rules are simple once separated out. Every non-zero digit counts. Zeros between non-zero digits count. Leading zeros never count, so 0.00456 has three significant figures, not five.

Trailing zeros are the awkward case. After a decimal point they count, because writing 4.50 claims precision to the hundredth. Before the point, with no decimal shown, they are ambiguous: 1500 might be measured to the nearest unit or the nearest hundred. This calculator takes them as not significant, which is the usual convention, and shows the scientific notation that removes the ambiguity entirely.

Rounding to significant figures is not the same as rounding to decimal places, which is why both appear. For 0.004560 three significant figures gives 0.00456, while three decimal places gives 0.005. In science and engineering the significant-figure version is almost always what is wanted, because it keeps the same relative precision regardless of the size of the number.

The page shows its working, not just its answer. Where there is a formula it is printed with your own numbers substituted in, so you can check the result rather than take it on trust -- which is the difference between a calculator you can use for something that matters and one you cannot.

Everything runs inside your browser. What you type is never uploaded, never logged and never stored, and the calculator keeps working if your connection drops after the page has loaded.

• Shows significant figures, rounded to sig figs, rounded to decimal places, scientific notation and rounding error together, so you are not running it twice
• A results table you can read across
• Prints the formula with your own figures substituted in
• Updates as you type, with no button to press and no page reload
• Copy the result in one click
• Free, no sign-up, and it runs entirely in your browser

The significant figures calculator is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:

• Rounding a lab measurement to the right precision
• Counting the significant figures in a reported value
• Comparing sig-fig rounding with decimal-place rounding
• Writing a number in scientific notation