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Significant Figures Calculator

Count the significant figures of a number and round it to the precision you need.

How it is calculated

The tool applies the standard counting rules to the number exactly as typed. Leading zeros never count; zeros between non-zero digits always count; trailing zeros count only if the number has a decimal point. So 1200 has 2 significant figures, but 1200.0 has 5. Signs and any exponent part (e notation) are ignored for counting. An all-zero entry such as 0.00 counts its decimals. The second result rounds the value to the number of figures you request (1 to 100; anything else returns no result) using general number formatting and keeps trailing zeros up to the requested count (0.5 to 3 figures gives 0.500, 1200 to 7 figures gives 1200.000). It may switch to a power-of-ten form, such as 1.20 × 10³, for very large or small values. Type the number as text, keeping trailing zeros.

Worked example

Enter 0.0045060 and ask for 3 figures. The leading zeros (0.00) are dropped, leaving 45060. A decimal point is present, so the trailing zero counts: the digits 4, 5, 0, 6, 0 give 5 significant figures. Rounding to 3 figures keeps 4, 5, 0; the next digit is 6, so the last kept digit rounds up to 1: 0.00451.

Try this example →

Common mistakes

  • Typing 0.0045060 as 0.004506 and losing a measured trailing zero, which changes the count from 5 to 4.
  • Counting leading zeros as significant; in 0.0045 only 4 and 5 count.
  • Assuming 1500 has 4 significant figures; without a decimal point the trailing zeros do not count, so it has 2.
  • Confusing significant figures with decimal places; 0.00451 has 5 decimal places but 3 significant figures.
  • Rounding intermediate steps of a long calculation; round only the final result.

Sources

About this calculator

This calculator counts the significant figures in a number — all the digits that carry real precision, following the standard rules for leading zeros (not significant), trailing zeros after a decimal point (significant), and numbers in scientific notation — and rounds the number to however many sig figs you need.

Science and engineering students use it to check lab report answers follow the correct precision rules, and anyone doing measurement-based calculations uses it to avoid implying more accuracy than the original data actually supports.

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  • Editorial team

    A handy rule for results: when you multiply or divide, the answer should carry as many significant figures as the least precise factor. So 4.2 times 3.1416 should be reported to two figures. The tool counts the digits as typed, so a whole number such as 1500 reads as 2 figures; if the trailing zeros were measured, type it as 1.50e3 to get 3. Which measurements do you most often have to round for lab work?

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