Unit Conversion for Students — Year 3 to GCSE with King Henry Trick
- King Henry Died By Drinking Cold Milk — the mnemonic for metric prefixes: kilo, hecto, deca, base, deci, centi, milli. This guide covers unit conversion from Year 3 through GCSE level.
Table of Contents
King Henry Died By Drinking Cold Milk — kilo, hecto, deca, base unit, deci, centi, milli. That mnemonic covers every metric prefix you need for school-level unit conversion. Once you have the prefix order, moving between metric units is just multiplying or dividing by 10.
The unit converter above handles exact calculations — use it to check your answers on worksheets and practice problems.
The King Henry Mnemonic — Metric Prefixes
| Letter | Word | Prefix | Multiplier | Example |
|---|---|---|---|---|
| K | King | kilo (k) | × 1,000 | 1 km = 1,000 m |
| H | Henry | hecto (h) | × 100 | 1 hm = 100 m |
| D | Died | deca (da) | × 10 | 1 dam = 10 m |
| B | By | base unit | × 1 | meter, gram, liter |
| D | Drinking | deci (d) | × 0.1 | 1 dm = 0.1 m |
| C | Cold | centi (c) | × 0.01 | 1 cm = 0.01 m |
| M | Milk | milli (m) | × 0.001 | 1 mm = 0.001 m |
To convert from a larger prefix to a smaller one: multiply (move decimal right). From smaller to larger: divide (move decimal left). Each step in the mnemonic = multiply/divide by 10.
Unit Conversion by Year Group
- Year 3–4: meters and centimeters, grams and kilograms, milliliters and liters. Basic × 100, × 1000 relationships.
- Year 5: converting between all metric units for length, mass, and capacity. Miles and kilometers introduced.
- Year 6: miles to km, reading and interpreting conversion graphs, using conversion factors. SATs questions often ask about miles to km using a ratio.
- Key Stage 3 (Years 7–9): compound units (km/h, g/cm³), dimensional analysis, converting areas and volumes.
- GCSE: full metric system, imperial conversions, compound unit problems, using conversion factors in multi-step problems.
Common School-Level Conversion Practice
| Convert | Method | Answer |
|---|---|---|
| 5 km to m | × 1000 | 5,000 m |
| 300 cm to m | ÷ 100 | 3 m |
| 2.5 kg to g | × 1000 | 2,500 g |
| 750 ml to L | ÷ 1000 | 0.75 L |
| 5 miles to km | × 1.609 | 8.05 km |
| 8 km to miles | ÷ 1.609 | 4.97 miles |
Conversion Graphs — How They Work
GCSE and Year 6 SATs exams often show a conversion graph — a straight line through (or near) the origin where the x-axis is one unit and the y-axis is the other. To use it: find your value on one axis, read across to the line, then read down (or up) to the other axis.
A miles-to-km graph at GCSE typically shows: 5 miles = 8 km. To convert 3 miles, read across from 3 on the miles axis to the line, then read down to km axis ≈ 4.8 km. The converter above gives the exact answer to check your graph reading.
Check Your Conversion Answers
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Open Unit Converter FreeFrequently Asked Questions
What is the King Henry mnemonic for metric units?
King Henry Died By Drinking Cold Milk — stands for kilo, hecto, deca, base unit, deci, centi, milli. Each step is a factor of 10.
How do you convert km to m?
Multiply by 1,000. 1 km = 1,000 m, so 5 km = 5,000 m. Moving from kilo (K) to base (B) in the mnemonic means moving right by 3 steps = multiplying by 10³ = 1,000.
What unit conversions appear in Year 6 SATs?
Year 6 SATs typically test miles to km conversion (using a ratio like 8 km ≈ 5 miles), metric unit conversions (g to kg, ml to L, cm to m), and reading from conversion graphs.
What is a GCSE unit conversion question?
GCSE questions often involve compound units like km/h to m/s, or multi-step conversions like converting cm³ to m³. They require knowing conversion factors and applying them systematically.
