That's not usually what is intended when liquor to grist ratios are given in the brewing literature. It's strictly how much water and grain is in the mash tun. They are usually given as a range and not a specific number to account for variations in brewhouse design. You have to figure out what works for your particular system. There's so much variation in homebrew systems and techniques that someone else's number is meaningless.
That's very true. We don't even measure our water. It comes in from the bottom of the keg and we slowly put in the malt as it rises. Once we have an inch above the floating grain bed we quit. We have a RIMS system so once again, systems are all different.
Whatever system you have try doing this:
Put five gallons in your kettle, or ten if doing ten gallons.
Boil for however long you normally boil. 60 minutes? 90 minutes?
Now measure what's left and subtract that from where you started.
Now you know how much wort you will need to end up at five or ten gallons.
Are you Batch sparging? Then you will be measuring your water for the mash only. Drain the mash and refloat it with sparge water and drain to the level required in the kettle.
If Fly sparging just sparge to the correct level in your kettle. This keeps the grains floating as you never let the water level below the grain level.
This just saves a lot of calculations and worries. Learning your system is what will make your beers more consistant.
By the way, if you don't hit your numbers after your boil then adjust the recipe to your system. You may need to add or subtract to get it right but don't mess with boil times etc. It you change your system then you might need to tweek the recipes too!
Happy brewing!