Just about
Definition 1 of 2
Pro Tip 1/3Timeframe Reference
Use 'just about' to suggest something will happen very soon. 
The train is just about to arrive.
Pro Tip 2/3Small Margin
Indicates there is only a slight difference or small remaining amount. 
She's just about tall enough to ride the roller coaster.
Pro Tip 3/3Uncertainty
Implies that the speaker is uncertain about the exact extent or amount. 
There were just about 20 people at the event.