--- title: "Scientific Quantities and Units" description: "Use scientific quantities with correct units: pair every measurement with its unit (metres, kilograms, seconds, newtons, joules), pick sensible prefixes like milli- and kilo-, convert between them, an" canonical: https://lightmysky.com/learn/science/scientific-quantities-and-units-mt_vdHqdaflog source: https://lightmysky.com/learn/science/scientific-quantities-and-units-mt_vdHqdaflog.md retrieved: 2026-10-19 --- > **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`. # Scientific Quantities and Units Use scientific quantities with correct units: pair every measurement with its unit (metres, kilograms, seconds, newtons, joules), pick sensible prefixes like milli- and kilo-, convert between them, and call chemicals by their proper scientific names Subject: Science · Area: Scientific Inquiry · Ages 11 to 14 Page: https://lightmysky.com/learn/science/scientific-quantities-and-units-mt_vdHqdaflog ## Ready when they can - Record measurements with the correct unit and symbol (e.g., 2.5 kg, 30 s, 1.2 m) - Convert between prefixed units when comparing or calculating (e.g., 2500 mL = 2.5 L, 0.4 km = 400 m) - Use proper chemical names for common substances in written work (e.g., sodium chloride rather than just 'salt') ## Lesson: Scientific quantities and units When recording mass, length, time or force, write the number with its unit. A mass written as 12 alone could mean grams or kilograms. The unit identifies the scale of the measurement. Length can be measured in metres, written m. Kilograms, written kg, measure mass. Seconds, written s, measure time. Choose a unit for the quantity you measured. Mass and time are different quantities. A value in kg describes mass, while a value in s describes time. They cannot be converted into each other. Newtons, written N, measure force; joules, written J, measure energy. Milli- means one thousandth of the named unit. There are 1000 millilitres in 1 litre. You may see ml or mL; both mean millilitres. To express a volume in L rather than mL, divide its numerical reading by 1000. For example, 1800 ÷ 1000 = 1.8, so 1800 mL = 1.8 L. The volume stays the same. Kilo- means one thousand. There are 1000 metres in 1 kilometre. To express a length in m rather than km, multiply its numerical reading by 1000. For example, 0.6 × 1000 = 600, so 0.6 km = 600 m. The length stays the same. Use an established chemical name when the substance's identity is known. Sodium chloride is the main compound in ordinary table salt. Salt also names a broader class of compounds, so the word alone does not identify sodium chloride. Baking soda is sodium bicarbonate. Compare measurements after expressing them in the same unit. A millinewton, mN, is one thousandth of a newton. Divide the numerical reading in mN by 1000 to get the reading in N. For example, 500 ÷ 1000 = 0.500, so 500 mN = 0.500 N. This is the same force, not 500 N. A kilogram contains 1000 grams. To express a mass in g rather than kg, multiply its numerical reading by 1000. For example, 1.25 × 1000 = 1250, so 1.25 kg = 1250 g. Defined conversions such as 1000 g = 1 kg do not change the physical mass. *(drawing: These factors compare each prefixed unit with the same named unit without a prefix.)* **Recap.** Record the quantity and unit, convert before comparing, and use chemical names only when the substance's identity is known. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Accurate Measurement](https://lightmysky.com/learn/science/accurate-measurement-mt_Psun-u_lPf) - [Converting measurement units (age 9+)](https://lightmysky.com/learn/mathematics/converting-measurement-units-age-9-mt_Zks8xyInSG) ## Opens up - [Uncertainty, Precision and Significant Figures in a Measurement](https://lightmysky.com/learn/science/uncertainty-precision-and-significant-figures-in-a-measurement-mt_HPc3OahYoV) - [Dimensional Analysis, Scaling and the Order-of-Magnitude Estimate](https://lightmysky.com/learn/science/dimensional-analysis-scaling-and-the-order-of-magnitude-estimate-mt_jXnXRMKnC3) - [Writing Science Reports](https://lightmysky.com/learn/science/writing-science-reports-mt_ThTbUuNb3p) - [Tables, charts, and graphs](https://lightmysky.com/learn/science/tables-charts-and-graphs-mt_YHsUhi4Prc)