Foundation reading 7 of 17 · ~4 min

Check units, size and rounding

Your goal: Check whether a calculated amount and its reported precision make sense.

A focused reading from The Mole and Molar Mass. Reading time is a Chem Help estimate.

Optional prerequisite review

Review if useful. These suggestions never lock a step.

Significant figures and reasonableness

Multiplication and division keep the smallest number of significant figures among the measured values, so 8.80 g divided by 44.01 g/mol gives 0.200 mol, three significant figures. Treat molar masses and NA as precise enough not to limit the answer, and round only at the end.

Then sanity-check the size: an amount smaller than one mole must give fewer than 6.022 × 10²³ particles, and a mass smaller than the molar mass must give less than one mole.

Subscripts and balanced-equation coefficients are exact counts, not measurements, so they never limit significant figures.

Sources and further reading

  • Chemistry 2e, Section 3.1: Formula Mass and the Mole Concept
    Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, et al. · OpenStax, Rice University · Chapter 3.1 · pp. Section 3.1 (web edition)
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    The current online Chemistry 2e edition lists CC BY-NC-SA 4.0. The source version used for this lesson and its applicable rights remain unverified.

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    Recorded attribution / license claim (applicability unverified): Adapted from "Chemistry 2e" by OpenStax, Rice University, licensed CC BY 4.0. Changes were made.

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  • SI base unit: mole (mol)
    Bureau International des Poids et Mesures (BIPM) · SI base units
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    CC BY 4.0 is verified for the SI Brochure, ninth edition updated in 2026. Its applicability to this lesson's linked webpage or source version has not been established.

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  • Definitions of SI Base Units
    National Institute of Standards and Technology (NIST)
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  • Chem Help Question Bank, Unit 1 Stoichiometry, topic "Definition of the mole/Mole conversions"
    Chem Help · Chem Help

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