Measurement and Conversion

Measurement

Measurement is comparing something unknown to a known standard to describe its size, amount, or extent. It helps us assign numbers to things like length, mass, time, temperature, or volume so we can understand, compare, and communicate them.

Measurement Systems

1. Imperial System (U.S. Customary System)

  • Not decimal-based; conversions are tricky.

  • Units:

    • Length: inch, foot, yard, mile

    • Weight: ounce, pound, ton

    • Volume: pint, quart, gallon

  • Where used: Mainly the United States, partly the UK.

2. Metric System (SI - International System of Units)

  • Decimal-based; units change by powers of 10 (easy to convert).

  • Used worldwide in science, industry, education, and daily life.

Base Units in SI:

Quantity

Unit

Symbol

Example

Length

meter

m

Height of a person → 1.65 m

Mass

gram

g

Bag of rice → 5 kg

Volume

mililiter

ml

Bottle of water → 1000ml

Temperature

°C

°C

Body temperature → 36.5°C

Time

second

s

Stopwatch → 45 s

Choosing Units:

Context

Best Unit

Reason

Measuring a classroom

meters

Medium-sized length

Measuring medicine dose

milligrams

Very small, precise quantity

Measuring road distance

kilometers

Large distance

Cooking liquid

milliliters

Small, precise measurement

Reporting body temp

°C

Standard in health & science

Using the incorrect unit can lead to errors, particularly in fields such as medicine, engineering, or aviation.

Scientific Notation

Used to write very large or very small numbers simply.
Form: m × 10ⁿ

  • m = coefficient (1 ≤ m < 10)

  • n = exponent (power of 10)

Example:

  • SARS-CoV-2 virus: 60 nm = 0.00000006 m = 6 × 10⁻⁸ m

Metric Prefixes

Prefixes show multiples or fractions of base units (kilo-, centi-, milli-, micro-, nano-, etc.).
Conversions:

  • Move decimal right → smaller unit

  • Move decimal left → larger unit