On mobile devices, bars are a visual representation of signal strength.
Each device calculates them differently. The number of bars a device is displaying doesn't always have a direct correlation to how fast an internet connection will be - there are far too many variables.
So we suggest instead running speed tests to check the quality of your internet connection and leaving bars to drown your sorrows when you can’t get online any other way. As an alternative, consider keeping a box of wine handy.