Measuring my boil kettle volume has always been a challenge.
First I tried notches on my brewing spoon. That worked OK, but getting an accurate measurement was difficult. I use a keggle, and leaning way in to see where 5ish gallons of wort crossed the spoon left a lot of room for error. It was easy to accidentally read a notch above or below the correct one.
Then I tried a sight glass. That worked until I was storing my keggles and one of them whacked into the tube and snapped it off. Not wanting to spend the money on another sight glass, I looked for a simpler solution that would allow me to accurately measure my boil kettle volume.
Threaded Rod Dipstick
I had the idea for this thing while building my hop filter which uses threaded metal rods. All you need is one of the longer threaded rods (36″), some hex nuts, and fender washers. Decide how many levels you want to mark. You'll use two nuts and one washer for each level. I marked off gallon levels 3-8.
Pour known amounts of water into your boil kettle to calibrate the dip stick. Then sandwich a fender washer between two hex nuts at each gallon mark. Tighten the nuts with using two wrenches so the washers are locked into place.
Here's a tip: put all of your nuts and washers on the rod ahead of time, then just thread them down to the appropriate spot as you calibrate. I made the mistake of securing my first washer then realized I'd have to thread the remaining ones all the way down the other end of the rod which would take much longer. Put them all on first, then adjust.
That's it! The benefit of this set up is that the washers make it super easy to read the wort levels. Much easier than notches on a spoon. Plus this whole thing cost about $7.
The only concern with my dipstick is that I'm using zinc plated steel which is known to rust easily. I've used this for a few batches and have had no problems yet. The fact that the dipstick is only submerged for 3 seconds and I dry it off right after should minimize the chance of rust, but if it becomes a problem then I can switch to stainless steel.
Why measure your boil volume?
I know some people don't worry about the boil volume as much as their mash and sparge volumes, but it really is important for calibrating your system and planning recipes
For one it lets you figure out your boil off rate. When I moved from Virginia to Denver my boil off rate increased from 1 gal/hr to 1.25 gal/hr. If I hadn't tested this beforehand by measuring my boil kettle volumes, I would have come up low on my final volume and high in final gravity.
By measuring your pre-boil volume you can also figure out how much wort you lost to grain absorption in the mash. If you take your mash + sparge water and subtract out your pre-boil volume + any losses to deadspace in your mash and hot liqour tanks, you have your grain absorption. You can use that number for future recipes.
Do you measure your boil kettle volumes? What do you use?