How much water goes in the mash?

Hello, I am about to start doing all grain. I have a recipe lined up and I am going to do a full boil of 6.5 gallons using my 8 gallon brew kettle. Question is, How much water is supposed to go into the mash tun? Im sure this varies depending upon what you want your OG to be, but to be honest I have no idea how to measure that or how to mess around with it. Thank you!

A safe rule of thumb is 1.25 quarts of water per pound of grain. Sometimes you go thicker and sometimes thinner, but this is a good ratio to start with.

I like 1.5 quarts of water per pound of grain. It seems to give me the best results, and it's easy to stir since it's not too thick nor too thin.

If you miss your temperature low, you can always add a little boiling water as well since it's not too much water to start with.

Then, you can sparge up to your boil volume (6.5 gallons).

For example, if you have 10 pounds of grain:

Mash in with 15 quarts. Stir well, and check the temperature. Out of that 15 quarts, the grain will absorb about a gallon of it. That means you'll get out 11 quarts of wort from the first runnings. If you want 6.5 gallons for your boil volume, you'd sparge with 3.75 gallons of sparge water.

I have also found that a slightly thinner mash with around 1.5 qts/lb water produces good results. I used to aim for 1.25 qts/lb, but Kai Troester's findings suggested that the thinner mash was beneficial. If you have the room in your mash tun, go thinner.

Another thing to recognize is that the mash thickness is another variable that sets mash pH. If you have high alkalinity water, then you might find that using a thicker mash helps avoid a high mash pH or reduces the amount of acid or acid malt you need to add to the mash. Conversely, if brewing with really low alkalinity water, then a thinner mash could help moderate the mash pH drop.

I use 1.5 so long as total grist is under about 14 lbs. for bigger beers if you keep it at 1.5 you end up with very little sparge water which I think hurts efficiency. I batch sparge and like to try to get similar volumes from first and second runnings. Beer Alchemy software defaults to this and on smaller beers will usually tell me to add a couple quarts to the mash right before starting to collect first runnings.

But today with my 23lb grain bill I needed to cut mash water down to 1.2 qt/lb in order to be able to sparge with about 4 gal..will collect 8 gal, boil down to 6, to end up wi 5.5 in the fermentor.

Okay perfect, I will aim for 1.5q per gallon I just finished making my mash tun and it has no leaks so Im excited! Just need to install the filter and im ready to start brewing!