You can use a bar magnet and a compass to get a rough idea of the strength of Earth's magnetic field.

What happened?

The force on a compass due to the Earth's magnetic field is relatively weak. Think of it as a gentle magnetic breeze.
However the field near the household magnet is dense like a tornado. Strong near the magnet and very weak as you move away.

Challenge 1: How strong is the Earth's magnetic field?

Find (or make) a compass & 1 household magnet.
Can you determine the exact distance at which the household magnet force equals that due to the Earth's magnetic field?
What does this distance tell us?