baffled by small amount of wort extracted (relative noob)

[jof]

Yep, if you have a separate mash tun, then I would continue sparge until I had the required volume of wort in the boiler.
Its how I do BIAB, mashing in the boiler and running wort into a FV to see volume.
then removing grain bag & putting the wort back into the boiler for the boil.

 

[Birdsnestbrewery]

Because every setup is different, different people have different boil-off, pipework losses etc. So I made a spreadsheet to do the water quantity calculations and refine it after each brew if necessary. I start from the desired fermenter volume and calculate the mash and sparge water needed, and use just that amount, allowing it all to drain down to my dead space (which is pretty low). I don't like instructions you see sometimes that say to sparge until you get the right amount of liquor or until the gravity is down to a certain value. That leaves too much uncertainty.
And water quantities in a recipe from someone else will not be 100% correct unless the original had exactly the same setup as you.

 

[An Ankoù]

I'm a bit baffled by this. I can see how or why the OP has got mixed up with the volumes, but shouldn't his wort by twice as strong, or at least a significantly higher OG than target OG. Or have I missed something here?

 

[Agentgonzo]

I'm a bit baffled by this. I can see how or why the OP has got mixed up with the volumes, but shouldn't his wort by twice as strong, or at least a significantly higher OG than target OG. Or have I missed something here?

You're not the only one. Best guess is that the mash was too thick and his efficiency suffered.
So then probably an excess of sugars left in the mash tun too.

 

[Stu's Brews]

You're not the only one. Best guess is that the mash was too thick and his efficiency suffered

This. By my estimation, the mash was somewhere between 2 and 5L short of what it should have been.

 

[MashBag]

+1 @foxy
Use full volume in an esky.
No sparge.
No dead space.
.... And preheat the esky before you start.