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Round to Significant Figures Calculator
Round any number to a specified number of significant figures. Shows before and after with a digit-by-digit breakdown.
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Try an Example
Pick a scenario to see how the calculator works, then adjust the values
Count Sig Figs
Count the significant figures in a measurement with trailing zeros
Key values: 0.00340 · count mode · 3 sig figs
Round to Sig Figs
Round a scientific measurement to 3 significant figures
Key values: 123456 · round to 3 · = 123000
Multiply with Sig Figs
Apply sig fig rules when multiplying two measured values
Key values: 12.5 x 3.2 · multiply · limiting factor
Rounding to Significant Figures
To round a number to significant figures:
- Start from the leftmost non-zero digit.
- Count digits — this is the last digit to keep.
- Look at the digit immediately after: if it's 5 or greater, round up; if less than 5, round down.
Examples
| Original | Rounded to 3 sig figs |
|---|---|
| 0.004567 | 0.00457 |
| 123,456 | 123,000 |
| 98.752 | 98.8 |
| 1.0049 | 1.00 |
Sig Fig Rules for Calculations
Multiplication & Division
The result has as many sig figs as the least precise input.
Addition & Subtraction
The result is rounded to the fewest decimal places(not sig figs) of any input.
Banker's Rounding (Round Half to Even)
When the digit to drop is exactly 5 (with no digits after it), standard rounding always rounds up, introducing a systematic upward bias. The scientific convention is round half to even:
- (round to even — 4 is even)
- (round to even — 6 is even)
- (round to even — 4 is even)
Why it matters: Over many calculations, always rounding 5 up accumulates error. Banker's rounding statistically balances rounding up and down, reducing systematic bias in aggregated results.
Common Mistake: Premature Rounding
Do not round intermediate results. Carry extra digits through the entire calculation and round only the final answer. Rounding at each step compounds rounding errors and can significantly change the result.
Frequently Asked Questions
How do I round to a specific number of significant figures?
Start from the leftmost non-zero digit and count the desired number of digits. Look at the next digit: if it is 5 or greater, round up; if less than 5, round down. For example, rounded to 3 sig figs becomes .
What is the difference between sig fig rules for multiplication and addition?
For multiplication and division, the result has as many sig figs as the least precise input. For addition and subtraction, the result is rounded to the fewest decimal places of any input, not the fewest sig figs.
What is banker's rounding?
When the digit to drop is exactly 5 with no digits after it, banker's rounding (round half to even) rounds to the nearest even number. For example, and . This prevents systematic upward bias in large calculations.
Why should I avoid rounding intermediate results?
Rounding at each step of a multi-step calculation compounds rounding errors and can significantly change the final answer. Always carry extra digits through the entire calculation and round only the final result to the appropriate number of significant figures.
How do I round 123,456 to 3 significant figures?
Starting from the leftmost digit, count 3 digits (1, 2, 3), then look at the next digit (4). Since 4 is less than 5, round down. The result is . The trailing zeros are needed as placeholders but are not significant.
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