--- title: "Density and How to Measure It" description: "Density is mass per unit volume, found by weighing and by measuring volume, including displacement for an awkward shape. Particle spacing explains why the same substance has a much lower density as a " canonical: https://lightmysky.com/learn/science/density-and-how-to-measure-it-mt_HrKI1-UzfI source: https://lightmysky.com/learn/science/density-and-how-to-measure-it-mt_HrKI1-UzfI.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Density and How to Measure It Density is mass per unit volume, found by weighing and by measuring volume, including displacement for an awkward shape. Particle spacing explains why the same substance has a much lower density as a gas. Subject: Science · Area: Matter & Materials · Ages 15 to 16 Page: https://lightmysky.com/learn/science/density-and-how-to-measure-it-mt_HrKI1-UzfI ## Ready when they can - Calculates density in kg per cubic metre or g per cubic centimetre and rearranges for mass or volume - Measures the volume of an irregular solid by displacement and reports its density - Uses particle spacing to explain why gases are usually much less dense than liquids and solids, while recognising exceptions to the solid-liquid density order ## Lesson: Packing mass into volume Density is mass per unit volume. Calculate it using density = mass / volume. Use g/cm3 for grams per cubic centimetre or kg/m3 for kilograms per cubic metre. Rearranging gives mass = density × volume and volume = mass / density. Keep mass and volume units consistent with the density units. *(drawing: A balance measures mass. The object's shape and material determine how you measure its volume.)* At equal mass, the object with the larger volume has the lower density. A sealed gas sample also becomes less dense if its volume increases: no gas leaves, so the same mass occupies more space. Heating does not always lower gas density. If a sealed rigid container keeps the volume fixed, its density stays the same. For a sinking solid that does not dissolve, react with water or absorb it, measure mass on a balance. Record the cylinder's initial water volume, fully submerge the solid, remove trapped bubbles and record the final volume. Read the bottom of the water meniscus at eye level. Solid volume = final reading - initial reading. Then divide mass by this volume. One millilitre equals one cubic centimetre. **Example.** A suitable solid has mass 72 g. The cylinder reads 40 cm3 before immersion and 64 cm3 after it. Its volume is 64 - 40 = 24 cm3, so density is 72 / 24 = 3 g/cm3. To find mass instead, multiply density by volume: a 12 cm3 sample with density 6 g/cm3 has mass 72 g. *(drawing: Subtract the initial reading from the final reading. The rise, rather than the final reading alone, gives the solid's volume.)* As in the particle model, particles in solids and liquids are close together. Gas particles are usually much farther apart, so the gas form of a substance usually has much less mass in the same volume. Solids are not always denser than liquids: ice is less dense than liquid water. Particle speed alone does not determine density; mass and occupied volume do. A fluid exerts an upward force called upthrust equal to the weight of fluid displaced. For the same displaced volume, a denser fluid gives greater upthrust. Seawater is denser than fresh water, so it provides greater upthrust for the same submerged volume. Ignoring surface tension, an object with lower average density than the liquid floats; one with greater average density sinks. **Recap.** Density = mass / volume. Displacement uses the change in water volume. Wider particle spacing usually lowers density; solids are not always denser than liquids. *Lesson, questions and flashcards written for this dataset.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [The Particle Model](https://lightmysky.com/learn/science/the-particle-model-mt_b6kZgqolEd) ## Optional connections - [Specific heat capacity as a material property](https://lightmysky.com/learn/science/specific-heat-capacity-as-a-material-property-mt_mXC9IKom3P) ## Opens up - [Pressure in Liquids and the Atmosphere](https://lightmysky.com/learn/science/pressure-in-liquids-and-the-atmosphere-mt_eLGNkEJAZl) - [Uncertainty, Precision and Significant Figures in a Measurement](https://lightmysky.com/learn/science/uncertainty-precision-and-significant-figures-in-a-measurement-mt_HPc3OahYoV) - [Stress, Strain and the Young Modulus](https://lightmysky.com/learn/science/stress-strain-and-the-young-modulus-mt_uWdqhWGT7Y)