Round to Significant Digits

All versionsROUNDLOG10

Rounding to a number of significant figures — 3 sig figs of 12,345 is 12,300; of 0.0④567 is 0.0457 — isn’t built in, but a short ROUND + LOG10 formula does it for numbers of any magnitude.

Quick formula: to round A2 to 3 significant digits:

=ROUND(A2, 3 - 1 - INT(LOG10(ABS(A2))))

LOG10 finds the number’s magnitude; the math converts “3 sig figs” into the right number of decimal places for ROUND.

Functions used (tap for the full reference guide):

ROUND LOG10

The example

The same precision (3 sig figs) across very different magnitudes.

	A	B
1	Value	3 sig figs
2	12,345	12,300
3	0.045678	0.0457
4	987.6	988

The formula

Three significant figures, whatever the size:

=ROUND(A2, 3 - 1 - INT(LOG10(ABS(A2)))) // 12,345 → 12,300; 0.045678 → 0.0457

How it works

The formula figures out where the significant digits start:

LOG10(ABS(A2)) gives the order of magnitude — for 12,345 it’s about 4.09; INT makes it 4.
For N significant figures you want to round at decimal place N - 1 - magnitude — here 3 - 1 - 4 = -2, i.e. the hundreds place.
ROUND(A2, -2) rounds 12,345 to 12,300 — exactly 3 significant figures.
For 0.045678 the magnitude is −2, so it rounds at the 4th decimal → 0.0457.

Guard against zero. LOG10(0) errors, so wrap it: =IF(A2=0, 0, ROUND(A2, 3-1-INT(LOG10(ABS(A2))))) returns 0 for a zero input.

Try it: interactive demo

Live demo

Enter a value and how many significant figures.

Value (A2)

Sig figs

Result:

Variations

Guard against zero

Avoid the LOG10(0) error:

=IF(A2=0, 0, ROUND(A2, 3-1-INT(LOG10(ABS(A2)))))

Different precision

Change the leading number for 2 or 4 sig figs:

=ROUND(A2, 2 - 1 - INT(LOG10(ABS(A2))))

Significant figures as a cell

Drive it from D1:

=ROUND(A2, D1 - 1 - INT(LOG10(ABS(A2))))

Pitfalls & errors

LOG10(0) and negatives. Zero errors and negatives need ABS (already in the formula). Guard zero with the IF shown above.

This rounds the value, not the display. The stored number changes — good for further math, but if you only want a display format, that’s a different tool.

Trailing significant zeros won’t show as a number (e.g. 12,300 with 3 sig figs vs 12,340). If you need to display a fixed count of sig figs, combine with TEXT.

Practice workbook

📊

Download the free Round to Significant Digits practice workbook

Values across magnitudes with the live sig-fig formula, the zero-guard and adjustable-precision variants, plus 4 challenges with answers. No sign-up required.

Frequently asked questions

How do I round to significant figures in Excel?

Use =ROUND(A2, N - 1 - INT(LOG10(ABS(A2)))) where N is the number of significant figures. LOG10 finds the magnitude so the rounding works for any size of number.

How do I avoid the LOG10 error on zero?

Wrap the formula in an IF: =IF(A2=0, 0, ROUND(A2, 3-1-INT(LOG10(ABS(A2))))). LOG10(0) is undefined, so zero is handled separately.

Does this change the number or just how it looks?

It changes the stored value via ROUND, so subsequent calculations use the rounded number. For display-only significant figures, combine with the TEXT function.

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Function references: ROUND · LOG10