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Significant Figures Calculator

Count or round significant figures.

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Reviewed by Dr. Alex M., Ph.D.
Last updated: November 2025

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Understanding Significant Figures

Significant figures are crucial in science and engineering to express the precision of a measurement. They prevent us from lying about how accurate our data really is.

💡 Expert Tips

The "Sandwich" Rule

Zeros appearing between two non-zero digits are ALWAYS significant. Think of them as the meat in a sandwich. 505 has 3 sig figs. 10001 has 5.

Leading Zeros Never Count

Zeros at the beginning of a number are just placeholders. 0.005 has only 1 significant figure (the 5). 0.025 has 2.

Exact Numbers

Counted numbers (like 5 apples) or defined constants (like 1 min = 60 sec) have infinite significant figures. They do not limit the precision of your calculation.

⚠️ Common Mistakes

Trailing Zeros without Decimal

The number "100" is ambiguous but usually has 1 sig fig. "100." (with the dot) has 3. "100.0" has 4. Be careful with that decimal point!

Rounding Too Early

When doing multiple calculation steps, keep extra digits in your calculator and only round at the very end. Rounding early introduces "rounding error".

Adding vs Multiplying

The rules are different! For multiplication, use the fewest sig figs. For addition, use the fewest decimal places. Don't mix them up.

❓ Frequently Asked Questions

What are significant figures? +

Significant figures (or sig figs) are the digits in a number that carry meaningful contribution to its measurement resolution. They include all non-zero digits, zeros between non-zero digits, and trailing zeros in a decimal number.

Are leading zeros significant? +

No. Leading zeros (like the 0s in 0.0052) are placeholders and are NOT significant. They just tell you how small the number is.

Are trailing zeros significant? +

It depends. If there is a decimal point, trailing zeros ARE significant (e.g., 5.00 has 3 sig figs). If there is no decimal point, they are usually NOT significant (e.g., 500 has 1 sig fig), unless specified otherwise.

Why do we use significant figures? +

They show the precision of a measurement. When you calculate with measured values, your answer cannot be more precise than your least precise measurement. Sig figs help keep track of this.

How many sig figs in 100? +

Usually 1. Without a decimal point, trailing zeros are ambiguous but generally treated as not significant. If written as '100.' (with a decimal), it has 3.

📚 References