How strong does an earthquake have to be to make itself felt?

In principle, near the epicentre, earthquakes with a magnitude of 2.5 or above can be felt. Only rarely do we receive earthquake notifications for events with a magnitude of just under 2. Earthquakes with magnitudes of 3 or higher are felt by large numbers of people; at magnitudes of between 4 and 5 they can be felt within a radius of up to 200 kilometres; and at magnitudes of 5 or more they can be felt up to several hundred kilometres away under some circumstances.

These increasing radii are due to the fact that the energy released by an earthquake increases by a factor of 30 per level of magnitude, making a magnitude 5 earthquake 30 times stronger than a magnitude 4 earthquake.

You can see how the energy released increases exponentially in the video.