What is the Significant Figures Calculator?

Count significant figures, round to N sig figs, and add, subtract, multiply, or divide with correct precision rules using this free significant figures calculator. Enter decimals with trailing zeros, whole numbers, or scientific notation — get step-by-step explanations for chemistry and physics homework. Runs instantly in your browser.

How to use the Significant Figures Calculator

Choose Count Sig Figs, Round, or an arithmetic mode (add, subtract, multiply, divide).
Enter your number(s) as written in the problem — include trailing zeros after a decimal.
For Round mode, set the target number of significant figures (1–15).
Review the result, raw calculation, and step-by-step sig-fig rules applied.
Copy the full summary for lab reports or homework.

Common use cases

Counting sig figs in chemistry lab measurements
Rounding experimental results to the correct precision
Checking addition and subtraction with decimal-place rules
Verifying multiplication and division homework answers
Teaching measurement uncertainty in introductory physics

Frequently asked questions

What are significant figures?: Significant figures (sig figs) are the meaningful digits in a measured or reported value. They reflect the precision of a measurement — for example, 1.50 has three sig figs because the trailing zero after the decimal is significant.
How do I count significant figures?: Non-zero digits always count. Zeros between non-zero digits count (105 → 3). Leading zeros do not count (0.0045 → 2). Trailing zeros after a decimal count (1.500 → 4). Trailing zeros in a whole number without a decimal are ambiguous (1200 may be 2, 3, or 4 sig figs).
What are the rules for multiplication and division?: The result is rounded to the same number of significant figures as the least precise input. Example: 6.8 × 2.34 → 16 (2 sig figs, not 15.912).
What are the rules for addition and subtraction?: The result is rounded to the same number of decimal places as the least precise input. Example: 1.2 + 3.45 → 4.7 (one decimal place), not 4.65.
Why does trailing zero ambiguity matter?: 1200 could mean 2 sig figs (1.2 × 10³) or 4 sig figs (1.200 × 10³). A decimal point after the zeros (1200.) or scientific notation (1.20 × 10³) clarifies intent. This tool flags ambiguous cases.

More Mathematical Tools

What is the Significant Figures Calculator?

How to use the Significant Figures Calculator

Choose Count Sig Figs, Round, or an arithmetic mode (add, subtract, multiply, divide).

Enter your number(s) as written in the problem — include trailing zeros after a decimal.

For Round mode, set the target number of significant figures (1–15).

Review the result, raw calculation, and step-by-step sig-fig rules applied.

Copy the full summary for lab reports or homework.

Frequently asked questions

What are significant figures?

Significant figures (sig figs) are the meaningful digits in a measured or reported value. They reflect the precision of a measurement — for example, 1.50 has three sig figs because the trailing zero after the decimal is significant.

How do I count significant figures?

Non-zero digits always count. Zeros between non-zero digits count (105 → 3). Leading zeros do not count (0.0045 → 2). Trailing zeros after a decimal count (1.500 → 4). Trailing zeros in a whole number without a decimal are ambiguous (1200 may be 2, 3, or 4 sig figs).

What are the rules for multiplication and division?

The result is rounded to the same number of significant figures as the least precise input. Example: 6.8 × 2.34 → 16 (2 sig figs, not 15.912).

What are the rules for addition and subtraction?

The result is rounded to the same number of decimal places as the least precise input. Example: 1.2 + 3.45 → 4.7 (one decimal place), not 4.65.

Why does trailing zero ambiguity matter?

1200 could mean 2 sig figs (1.2 × 10³) or 4 sig figs (1.200 × 10³). A decimal point after the zeros (1200.) or scientific notation (1.20 × 10³) clarifies intent. This tool flags ambiguous cases.