How many sig figs for uncertainty: one or two?

Usually report the uncertainty with one significant figure, but you can use two significant figures when the first digit is one or two for better accuracy.

Think of the uncertainty like how sure you are about a measurement; we usually keep it simple with one significant figure so the number is easy to understand. If the uncertainty starts with a one or a two, sometimes using two significant figures gives a clearer picture without adding confusing detail. Always round the measured value to the same decimal place as the uncertainty so the numbers line up and make sense together. This keeps the reported value and its uncertainty consistent and easy to compare.

A common mistake is keeping too many digits in the uncertainty, which makes the reported precision look false and can confuse readers; fix that by rounding the uncertainty to one significant figure unless the first digit is one or two. Another error is failing to round the measured value to the same place as the uncertainty, which makes the pair inconsistent; correct this by aligning the decimal places before reporting. Some students write the uncertainty with extra leading zeros or use scientific notation inconsistently, so check formatting and adjust both numbers the same way.

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Uncertainty Sig Figs: Use One or Two

1. Use one significant figure for uncertainty
2. Use two sig figs if leading digit is 1 or 2
3. Round measured value to match uncertainty
4. Align decimal places for consistency

Common Uncertainty Reporting Mistakes

1. Keeping too many digits in uncertainty
2. Not aligning value with uncertainty
3. Using inconsistent formatting or zeros

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