How to Round to Significant Figures

Q: How do you round 3.456 to 2 significant figures?

The first two sig figs are 3 and 4. The next digit is 5 — so you round up. 3.456 rounded to 2 sig figs is 3.5.

Q: What is the difference between rounding to decimal places and rounding to significant figures?

Decimal places count digits after the decimal point regardless of significance. Significant figures count all meaningful digits starting from the first non-zero digit. Rounding 0.0034 to 2 decimal places gives 0.00. Rounding to 2 sig figs gives 0.0034.

Q: How do you round 0.006782 to 2 significant figures?

The first significant digit is 6 (the leading zeros are not significant). The second is 7. The next digit is 8 — round up. The answer is 0.0068.

Q: Does rounding change the number of significant figures?

Yes — that is the point. You are deliberately reducing the number to a target sig fig count. If you round 3.456 to 2 sig figs, the result 3.5 has exactly 2 sig figs.

Q: What happens to trailing zeros when you round to significant figures?

If rounding produces trailing zeros after a decimal point, you must keep them — they are significant. For example, 2.996 rounded to 3 sig figs is 3.00, not 3. The trailing zeros show the precision of the result.

Q: How do you round a number like 2.996 to 3 sig figs without losing precision in the display?

When rounding causes a carry that produces trailing zeros, keep them. 2.996 → 3.00. If writing as a whole number, use scientific notation: 3.00 × 10⁰ to make the sig fig count unambiguous.

A step-by-step method for rounding any number to a target sig fig count — with worked examples, decimal cases, and common mistakes.

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Reviewed by the Sig Figs Calc Editorial Team · Last updated April 2025 · See methodology

What does rounding to significant figures mean?

Rounding to significant figures means reducing a number so it has a specific number of meaningful digits. The goal is to express a measurement at a chosen level of precision — no more, no less.

This is different from rounding to decimal places. Rounding to 2 decimal places always gives you 2 digits after the decimal point. Rounding to 2 significant figures gives you 2 meaningful digits — wherever those digits happen to fall.

Key distinction

Rounding 0.006782 to 2 decimal places → 0.01
Rounding 0.006782 to 2 sig figs → 0.0068

How to round to significant figures — step by step

Identify the significant figures

Apply the sig fig rules to find which digits are significant. The target sig fig count tells you which position you are rounding to.

Find the cut point

Count to the target sig fig position from the first significant digit. This is where you will round. Everything after this position will be removed or zeroed.

Look at the digit immediately after the cut point

This is the deciding digit. If it is 5 or greater, round the last kept digit up by 1. If it is 4 or less, leave the last kept digit unchanged.

Remove or replace the remaining digits

For digits after the decimal point: simply drop them. For digits before the decimal point: replace them with zeros to preserve the magnitude of the number.

Check your result

Verify the result has exactly the target number of sig figs. If you rounded 3456 to 2 sig figs, the answer is 3500 — and 3500 without a decimal is ambiguous, so consider writing 3.5 × 10³.

Rounding 3456.7 to 1, 2, 3, and 4 significant figures

See how the same number rounds differently depending on the target.

1 sf3000First sig fig is 3. Next digit is 4 — round down. Replace 456.7 with zeros.

2 sf3500Second sig fig is 4. Next digit is 5 — round up. 3456.7 → 3500.

3 sf3460Third sig fig is 5. Next digit is 6 — round up. 3456.7 → 3460.

4 sf3457Fourth sig fig is 6. Next digit is 7 — round up. 3456.7 → 3457.

⚠️ Note on trailing zeros in integers

When you round an integer and get trailing zeros (like 3000 or 3500), those zeros are ambiguous. Use scientific notation to be precise: 3.5 × 10³ clearly has 2 sig figs. See Rule 5 on trailing zeros →

Rounding decimals to significant figures

Decimals with leading zeros require careful counting — the count always starts at the first non-zero digit.

0.006782→ 2 sf0.0068First sig fig is 6 (position 3 after decimal). Second is 7. Next digit is 8 — round up. 0.006782 → 0.0068.

0.00340→ 2 sf0.0034First sig fig is 3. Second is 4. Next digit is 0 — round down. Drop the trailing zero.

12.345→ 3 sf12.3First three sig figs: 1, 2, 3. Next digit is 4 — round down. 12.345 → 12.3.

0.09985→ 3 sf0.0999First three sig figs: 9, 9, 8. Next digit is 5 — round up. 8 becomes 9.

2.996→ 3 sf3.00First three sig figs: 2, 9, 9. Next digit is 6 — round up. 2.996 → 3.00. Keep trailing zeros to show precision.

Significant figures vs decimal places — what is the difference?

This is one of the most common points of confusion. The table below shows both counts for the same numbers.

Number	Sig figs	Decimal places	Why sig figs differ
3.456	4	3	All 4 non-zero digits
0.0034	2	4	Only 3 and 4
100.00	5	2	1, 0, 0, 0, 0 all count
1200	2 (min)	0	1 and 2 (trailing zeros ambiguous)
0.050	2	3	5 and trailing 0

The key insight: sig figs start counting from the first meaningful digit. Decimal places always start from the decimal point. For numbers like 0.0034, these are very different.

Common rounding mistakes

✗ Starting the count from the wrong digit

Always start counting from the first non-zero significant digit, not from the decimal point or the leftmost digit. In 0.00340, the count starts at 3, not at the first 0.

✗ Forgetting to add trailing zeros when needed

If you round 2.996 to 3 sig figs, the answer is 3.00 — not 3. The trailing zeros are significant and must be shown to communicate the correct precision.

✗ Rounding twice

Round in one step, not two. If you need 2 sig figs from 3.456, go directly to 3.5 — do not round to 3.46 first and then to 3.5.

✗ Confusing sig fig rounding with decimal place rounding

Rounding 0.006782 to 2 decimal places gives 0.01. Rounding to 2 sig figs gives 0.0068. These are completely different operations.

Check your rounding with the calculator

Use the Round tab to enter any number and target sig fig count. The calculator shows the rounded result and explains each step.

Open the Round calculator →

Frequently asked questions

Common questions about rounding to significant figures.

How do you round 3.456 to 2 significant figures?

What is the difference between rounding to decimal places and rounding to significant figures?

How do you round 0.006782 to 2 significant figures?

Does rounding change the number of significant figures?

What happens to trailing zeros when you round to significant figures?

How do you round a number like 2.996 to 3 sig figs without losing precision in the display?

Explore rules, examples, and operation guides.

Sig Figs Calculator

Round any number using the calculator — with steps shown.

Significant Figures Rules

The 7 rules that determine which digits are significant.

Addition & Subtraction

How rounding applies in addition and subtraction.

Multiplication & Division

How rounding applies in multiplication and division.

Scientific Notation

Rounding the coefficient in scientific notation.

Examples Hub

Rounding examples and more — browse by category.