Compound Measures: Speed, Density and Pressure

Compound measures combine two different units to describe a rate or relationship. The three compound measures you need for AQA GCSE Mathematics are speed, density, and pressure. This lesson covers the formulae, unit conversions, and worked examples for each.

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What Is a Compound Measure?

A compound measure is a measure that involves two or more different units. For example, speed is measured in miles per hour (mph) — it combines distance (miles) with time (hours).

Compound Measure	Formula	Common Units
Speed	Speed = Distance / Time	m/s, km/h, mph
Density	Density = Mass / Volume	g/cm cubed, kg/m cubed
Pressure	Pressure = Force / Area	N/m squared (Pascals), N/cm squared

Exam Tip: You can rearrange each formula using the formula triangle method. Cover the quantity you want to find, and the remaining two quantities show you the calculation.

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Speed, Distance and Time

The Formulae

• Speed = Distance / Time
• Distance = Speed x Time
• Time = Distance / Speed

Formula Triangle