How to accurately compute fermenter capacity

[njohnsoncs]

So it has been mentioned on these forums that fermenters with labeled capacities (often in gallons) are notoriously inaccurate. I'm wondering what a good way to accurately compute the capacity is, say, in 1 gallon increments? I could try to use a kitchen measuring cup but how do I know it is accurate?

What do you guys use as your reference when measuring capacity in your fermenters?

 

[dyqik]

Weigh your water out (if you do all-grain, you probably have scales capable of accurately measuring the weight of at least 1 gallon of water), being careful to correct for the temperature of the water. Add 1 gallon at a time, and mark off 1 gallon increments.

 

[Morrey]

I did this just last week when I measured a SS conical fermenter to test/check the volume markings. While I was at it, I also checked the sight glass markings on my boil kettle.

The fermenter was off by around .2 Gallons when filled with 7 Gallons of water, whereas the boil kettle was darn near dead on the money.

I had a gallon jug of distilled water I had just emptied mixing with glycol in my chiller. Filling this empty container 7 times as my measuring jug, I filled the fermenter. After each gallon, I looked to see any errors and jotted down that offset. After that, I poured the water into my boil kettle for a measured test. This may not be the most scientific approach to the "n"th degree, but it shows me the offset I need when calculating vol into fermenter for efficiency percentages.

I did use the water for watering plants afterwards...eco minded.

 

[njohnsoncs]

Weigh your water out (if you do all-grain, you probably have scales capable of accurately measuring the weight of at least 1 gallon of water), being careful to correct for the temperature of the water. Add 1 gallon at a time, and mark off 1 gallon increments.

I thought using the weight of a gallon of water might be the way to go. I'll have to try this. Thanks!

 

[tjmac5071]

Fyi the 1 gallon jugs are larger than 1 gallon... Weight is the way to go, it's how I measure all of my water for brewing

 

[brandonlovesbeer]

I fill up my carboys 1 gallon at a time and mark them with a Magic Marker at each gallon mark.
I'm planning to try etching the glass in the future.

 

[brandonlovesbeer]

Fyi the 1 gallon jugs are larger than 1 gallon... Weight is the way to go, it's how I measure all of my water for brewing

That's an interesting idea.

 

[dyqik]

Fyi the 1 gallon jugs are larger than 1 gallon... Weight is the way to go, it's how I measure all of my water for brewing

You could weigh the gallon jug, then jug plus water, and mark it at the 1 gallon level to make filling it back up to 1 gallon (checking against the weight again) quicker.

 

[Morrey]

Fyi the 1 gallon jugs are larger than 1 gallon... Weight is the way to go, it's how I measure all of my water for brewing

Probably so. I have always used 8.34 pounds for a gallon of water, so I weighed a gallon jug (minus tare) of water to 8.34 pounds and marked that level with a sharpie pen. I assumed this would be a fairly accurate way of testing to use a simple container I had available.