Directly, a one-metre square has sides of one thousand millimetres, so its area is \(1000\times1000=1000000\text{ mm}^2\).

Alternatively, one square metre contains ten thousand square centimetres, each containing one hundred square millimetres.

Thus \(10000\times100=1000000\text{ mm}^2\).

Answer

Both methods give one million square millimetres.