If you make curtains to the exact width of the pole they won't meet in the middle, as they will naturally spring back a bit and there will be nothing extra for them to overlap.
We therefore add an amount for ease and overlap when calculating how wide to make the pleated curtain panels.
There are various figures curtain makers use for this (some adding 10% , others 2cm per 50cm of pole for ease plus overlap etc), What is important though is that you don't overdo it. If you add too much, the extra doesn't evenly spread across the curtain, it just means a section of curtain stays stacked back at each side when you pull them closed.
In the workshop for calculating ease and overlap when making our hand pleated curtains, we basically add 4cm to each curtain for the overlap (that will create an 8cm overlap as each curtain will pass the middle by 4cm in opposite directions) plus we add 5% of pole covered by the curtain.
Thus for a PAIR of curtains, we would add the following for ease and ovelap to EACH curtain.
|Pole Length||Ease + Overlap per curtain|
Note for a pencil pleat (tape) headed curtain you can always adjust the ease and overlap, by loosening the tape off or pulling it tighter. Therefore we generally use a figure of 5cm ease and overlap per curtain then adjust if necessary when the curtain is hung.