Measures and accuracy: use standard units of mass, length, time, money and other measures (including standard compound measures) using decimal quantities where appropriate

The idea

This skill means choosing and applying the correct standard unit for mass (g, kg, tonne), length (mm, cm, m, km), time (s, min, h), money (£, p) and other measures, and handling decimal quantities correctly. You must also work with standard compound measures such as speed (m/s, km/h), density (g/cm³, kg/m³) and pressure (N/m²), where the unit is formed from two or more base units. For example, a journey of 12.5 km in 0.25 h gives 12.5 ÷ 0.25 = 50 km/h. When converting, multiply or divide by the correct power of ten or by 60 for time; keep decimal places consistent with the context.

What earns the marks

• Selects the correct standard unit for a given mass, length, time or money quantity, for example kg for a person's mass or m for a room length.
• Converts between related units using the correct factor, for example 1 kg = 1000 g, 1 m = 100 cm, 1 h = 60 min, £1 = 100 p.
• Uses decimal quantities correctly when calculating with measures, for example 2.5 kg + 0.75 kg = 3.25 kg.
• Recognises and uses standard compound measures, for example speed = distance ÷ time with units such as m/s or km/h.

Common mistakes and how to put them right

• Mixing units within one calculation, such as adding 250 g to 1.2 kg without converting.

  Put it right by converting all quantities to the same unit first, for example 250 g = 0.25 kg, then 0.25 + 1.2 = 1.45 kg.

• Using 100 as the conversion factor for time.

  Put it right by using 60, so 1.5 h = 1 h 30 min = 90 min, not 150 min.

• Treating a compound unit as a single unit, for example writing speed as just m.

  Put it right by writing the full compound unit such as m/s or km/h.

Exam tips

• Underline the unit required in the question and convert every given quantity to that unit before calculating.
• For compound measures, write the formula and substitute with units, then simplify the units to check they match the answer options.
• Estimate the size of the answer first; if an option is ten or a hundred times too large or small, it is likely a conversion error.