If you want 6 gallons in your kettle for boil, you'll need to also compensate for water absorbed by the grain and dead space in your mash tun. As for "weak", you'll never know unless you measure the gravity of your runnings, etc. Hydrometer or refractometer.
"Beer, well respected and rightly consumed, can be a gift of God. It is one of his mysteries, which it was his delight to conceal and the glory of kings to search out."
The Search for God and Guinness by Stephen Mansfield