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Significant figures calculator

Count significant digits and round a measured number to your chosen significant-figure count.

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Answer

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Count significant digits and round a measured number to your chosen significant-figure count.

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Precision and calculation record
Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.
Saved scenario
Save the current answer, then change an input to compare. This clears when you leave.
Formula and assumptions
Leading zeros are ignored. Trailing zeros count only when a decimal point is written; whole-number trailing zeros are treated as placeholders. For all-zero decimals, written decimal places are counted by convention. Halfway rounding is away from zero. An ordinary integer result does not encode its trailing-zero significance.
Whole-number and finite-decimal arithmetic is exact within the stated input limits. Any requested rounding uses the selected setting. Thousands separators such as 1,000 are accepted; use a dot for decimals.
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Use +, −, ×, ÷, parentheses and %. A percentage is divided by 100. This does not change the main tool.
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Using Significant figures calculator
Count significant digits and round a measured number to your chosen significant-figure count.
Leading zeros are ignored. Trailing zeros count only when a decimal point is written; whole-number trailing zeros are treated as placeholders. For all-zero decimals, written decimal places are counted by convention. Halfway rounding is away from zero. An ordinary integer result does not encode its trailing-zero significance.
Next: Scientific notation calculator
A worked example
Example inputs: measured number = 0.00450, significant figures for rounding = 2. Significant-figure count = 3.
Before you use the result
Leading zeros are ignored. Trailing zeros count only when a decimal point is written; whole-number trailing zeros are treated as placeholders. For all-zero decimals, written decimal places are counted by convention. Halfway rounding is away from zero. An ordinary integer result does not encode its trailing-zero significance. Whole-number and finite-decimal arithmetic is exact within the stated input limits. Any requested rounding uses the selected setting.
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ToolOctopus. “Significant figures calculator.” Updated 2026-09-20. https://tooloctopus.com/significant-figures-calculator.
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