Significant Figures Calculator

1. Enter the number you want to round.
2. Enter how many significant figures to keep.
3. Read the rounded value, kept to that many meaningful digits.
4. See the result in scientific notation and the change from the original.

Here is what each result means:

Significant figures are the meaningful digits in a number, the ones that carry real information about its precision. They start at the first nonzero digit and run to the last digit you keep. So 0.00457 has three significant figures, since the leading zeros only place the decimal point and do not count.

Significant figures matter most in science and engineering, where a measurement is only as precise as the tool that made it. Reporting too many digits claims a precision you do not have, while too few throws away real information. Rounding to a sensible number of significant figures states the precision honestly.

It rounds the number so that only the chosen count of meaningful digits remains.

1. Find the first nonzero digit, where counting begins.
2. Keep that many digits and round the next one up or down.
3. Fill any place values with zeros or a power of ten to hold the size.

To round to a fixed number of decimal places instead, use the rounding calculator, and for the compact power-of-ten form, the scientific notation calculator.

Round 0.0045678 to three significant figures, and 12,345 to two.

Calculation: for the small number, counting starts at the 4, so three figures are 4, 5 and 6, and the next digit 7 rounds the 6 up to 7, giving 0.00457. For 12,345, the first two figures are 1 and 2, and the next digit 3 rounds down, giving 12,000, or 1.2 times 10 to the 4th.

A few simple rules decide which digits count.

Trailing zeros in a whole number, like 1500, are ambiguous, which is why scientific notation is used to state the precision clearly.

The two ways of rounding answer different questions.

Significant figures count meaningful digits from the first nonzero one; decimal places count digits after the point. Pick the one your task needs.

The Count You Choose

Fewer significant figures round the number more and claim less precision.

Where the Digits Start

Leading zeros never count, so a small number keeps its meaningful digits far to the right.

The Next Digit

The first digit dropped decides whether the last kept digit rounds up or stays.

Science and Lab Work

Report a measurement to the precision your instrument actually supports.

Engineering

Round results to a sensible number of meaningful digits for a spec or drawing.

Homework

Check a rounding to a stated number of significant figures.

1. Counting Leading Zeros

Leading zeros only place the decimal point. In 0.0047, counting starts at the 4.

2. Confusing Figures with Decimals

Two significant figures is not the same as two decimal places. Decide which the task needs.

3. Rounding in Steps

Round once to the final count. Rounding twice can push the answer the wrong way.

4. Dropping Needed Precision Early

Keep extra digits through a calculation, then round the final answer.

5. Ambiguous Trailing Zeros

1500 could be two to four significant figures. Scientific notation removes the doubt.

The rounding is exact for the count chosen; only tiny floating-point effects can appear.

They are the meaningful digits in a number, starting at the first nonzero digit. They show how precise a value is. So 0.00457 has three significant figures, since the leading zeros do not count.

Count from the first nonzero digit, keep the number you want, and round the next digit up or down. This tool rounds 0.0045678 to three significant figures as 0.00457.

No. Leading zeros only place the decimal point and carry no precision. In 0.0047, only the 4 and 7 are significant, so it has two significant figures.

Trailing zeros after a decimal point count, since they show measured precision, so 2.50 has three. Trailing zeros in a whole number like 1500 are ambiguous, which scientific notation resolves.

Significant figures count meaningful digits from the first nonzero one. Decimal places count digits after the point. For 0.04059, two significant figures is 0.041, while two decimal places is 0.04.

They state precision honestly. Reporting too many digits claims accuracy you do not have, while too few loses real information. They matter most in science and engineering.

This tool rounds to a count you choose. It does not count the figures in a plain number, because a number cannot show whether its trailing zeros are significant.

Match the precision of your data or instrument. Measurements are usually reported to two, three or four significant figures, depending on how precisely they were made.

No. The calculation runs in your browser and nothing you enter is stored or sent anywhere, unless you choose Save, which keeps the result only on this device.

• Significant figures (Wikipedia).
• Significant figures explained (Maths Is Fun).
• Rounding numbers (Maths Is Fun).