Sig Fig Calculator

Sig fig calculator at a glance#

Significant figures, or sig figs, are the digits in a number that carry real precision. Four rules set the count: every non-zero digit counts; zeros between non-zero digits count; leading zeros never count; trailing zeros after a decimal point count. The calculator above counts the significant figures in a number and rounds it to a chosen number of them.

How many significant figures does a number have?#

Apply the four rules digit by digit. So 0.00230 has 3 significant figures: the leading zeros do not count, while 2, 3 and the trailing 0 after the decimal do. The number 502 has 3, because the zero sits between two non-zero digits. A plain whole number like 1200 is ambiguous, since trailing zeros with no decimal point may or may not count; writing it as 1.20 x 10^3 pins the count at 3.

How do you round to a number of significant figures?#

Keep the digits you need, then look at the next digit. If it is less than 5, leave the last kept digit as it is; if it is 5 or more, raise it by 1. So 45.678 rounded to 3 significant figures is 45.7, because the next digit, 8, is 5 or more, so the 6 rounds up to 7. Rounding the same number to 2 significant figures gives 46.

Enter your number in the calculator above to count its significant figures, and set a target count to round it, in standard, e-notation or scientific format. Round once at the end of a longer calculation rather than at each step, so small rounding shifts do not build up.

When the count matters#

A significant figure count tells you how much of a number is real measurement and how much is just placeholder. A length recorded as 3.0 cm claims precision to a tenth; the same length as 3.00 cm claims precision to a hundredth, even though both look like "3". The count, not the digit itself, carries that information.

That is why the count is a property of how a number is written. Writing 0.50 instead of 0.5 is a deliberate statement that the value is good to two figures, not one.

Three counting cases people get wrong#

Leading zeros never count, no matter how many there are: 0.00230 has 3 significant figures, not 5. A zero between non-zero digits always counts: 4005 has 4. A trailing zero only counts when a decimal point is present, so 50 has 1 figure that is clearly significant, while 50. and 50.0 have 2 and 3.

The bare whole number 1200 is the classic trap: with no decimal point its trailing zeros are ambiguous, so it could be read as 2, 3 or 4 figures. Write it as 1.2 × 10³, 1.20 × 10³ or 1.200 × 10³ to say exactly which.

Sig fig calculator FAQ#

How many significant figures does 0.045 have?#

Two. The leading zeros before the 4 do not count, so only the 4 and the 5 are significant. By the same rule 0.00230 has 3 figures, because the trailing zero after the decimal does count.

How do you round to 3 significant figures?#

Keep the first three significant digits, then look at the next one. If it is 5 or more, round the third digit up; if it is below 5, leave it. So 45.678 to 3 significant figures is 45.7, and 0.012348 to 3 significant figures is 0.0123.

Do trailing zeros count as significant figures?#

Only when there is a decimal point. 4500 written plainly is ambiguous, but 4500. and 4500.0 fix the count at 4 and 5. After a decimal, every trailing zero counts, so 2.00 has 3 figures.

How many significant figures are in scientific notation?#

Count only the coefficient; the power of 10 never adds figures. So 3.45 × 10⁵ has 3 significant figures and 6.700 × 10⁻² has 4. This is the cleanest way to state a count with no ambiguity.

Do exact counts have significant figures?#

Exact numbers, like 12 eggs in a dozen or a defined conversion such as 1 inch = 2.54 cm, are treated as having unlimited significant figures. They never limit the precision of a result, so only your measured values set the figure count.