A bottle of water says 500 ml on the label. A big carton of juice says 1 litre. How many of those water bottles do you think it would take to fill the carton right up?

Have a think before any hands go up. What is it about the two labels that makes them tricky to compare?

Watch one full rename on the board first, then notice the pattern on each display.

Worked example: rename 1 l 500 ml into millilitres only.

1. Turn the whole litre into millilitres: 1 l = 1,000 ml (multiply by 1,000).
2. Add the leftover millilitres: 1,000 + 500 = 1,500 ml.

So 1 l 500 ml and 1,500 ml are the same amount, just written two ways.

Now look at each display. Have a prediction ready: will the number get bigger or smaller, and are we multiplying or dividing by 1,000?

Today we work through these together on the board: first we rename 3 l into millilitres, then 4,000 ml back into litres, then the mixed amount 1 l 250 ml into millilitres, and finally 2,500 ml back into litres and millilitres. For the mixed one, we combine it by hand first the way we just did , 1 litre is 1,000 ml, add the extra 250 ml, then set that on the converter. The mixed ones catch people out, so we will say each one aloud before we check it.

Today we work through these numbers together at the board: 4 l → ml (a clean times a thousand), then 6,000 ml → l (a clean divide by a thousand), then the mixed amount 1 l 250 ml, combine it by hand first the way we practised, then convert that back to litres on the board to check, and finally 2,750 ml → l and ml. Predict where the number will land before we check each one.