Getting accurate volume measures

[raspsu1]

How does everyone go about getting accurate volume measurements? It’s seems that ever piece of equipment has volumes labeled on it, but none of them seem to match up 100%. I have a pot with quart marking, a cooler with gallon markings, a fermenting bucket with gallon markings, a plastic pitcher with quart markings.

If I fill the pot to 4 quarts and put it in the cooler, there is no guarantee it will hit the 1 gal mark. If I fill the pitcher to 4 quarts, it doesn’t match the 4 quarts in the pot it actually comes out as more.

So what’s the deal? How do you all handle taking accurate measurements when we have equipment with markings but they don’t all seem to line up? Anyone else have that issue?

[s_scoggin]

for each of my 2 kettles i brewed with gallon jugs of spring water once. this way i could add gallon by gallon and mark a wooden stick each gallon for each individual kettle.

so when i add water to a kettle i keep the stick in there to get the volume i want

thats what i do, seems to work well

not my picture. but this may help: http://www.flickr.com/photos/awinner/5760578456/

[raspsu1]

I actually have a stainless steal BBQ skewer from lowes that I marked and use to have my two pots calibrated together. But for example, if I put 4.25 gals in the pot, heat up to mash temp, put in the cooler, I’ll come in under 4.25 gals in the cooler. So I’m not sure which one to trust.

[baratone_brewer]

Aluminum flat bar that I marked by filling my keggles a gallon at a time. I trust the ones that I marked.

[slothrob]

Instead of trying to accurately fill a measuring cup repeatedly, I use π(r^2)h=volume and a dipstick for my kettles. I measure the pots to determine their diameter (then, radius) in cm, then use a dipstick marked in cm in the working range of my brewing. I printed out a conversion table that makes it easy to get an accurate volume very quickly from the dipstick.

[raspsu1]

@Slothrob

Instead of trying to accurately fill a measuring cup repeatedly, I use π(r^2)h=volume and a dipstick for my kettles. I measure the pots to determine their diameter (then, radius) in cm, then use a dipstick marked in cm in the working range of my brewing. I printed out a conversion table that makes it easy to get an accurate volume very quickly from the dipstick.

That’s a formula I thought I’d never use again (like so much we use in homebrewing that we learned in school and you never thought you’d use).

So what is the conversation then to the cm to say gallons or whatever measure you are using?

[breslinp]

1mL = 1cm^3

[conroe]

You have to compensate for temperature expansion

Thermal expansion

. Markings can be wrong too.

[raspsu1]

[quote=“Conroe”]You have to compensate for temperature expansion

Thermal expansion

. Markings can be wrong too.[/quote]

Yes, already prepared and take that into consideration.

[conroe]

You can also just weigh it. A pint’s a pound.

[raspsu1]

I’ve tried the cm^3 to ml calculation on several of my brew items and it just doesn’t work out. I’m off by around a cm on each item. So let me see if I’m doing this correctly.

I’ve taken a pot that is marked in quarts. The Diameter of the pot is 30.5 cm, so that makes the radius 15.25 cm.

So using the forumula pi*(r^2)*h, that would mean each centimeter of height would be around 730 ml or around .77 quarts (I’ve rounded these numbers).

Its easier to read the quarts toward the top of the pot. If I measure where the 16 quart line is, it is around 19.75 cm. However, using the formula above, I’d need to be closer to 20.75 to get 16 quarts.

The error is even worse on my cooler.

Hmmmmm…

[baratone_brewer]

@Slothrob

Instead of trying to accurately fill a measuring cup repeatedly, I use π(r^2)h=volume and a dipstick for my kettles. I measure the pots to determine their diameter (then, radius) in cm, then use a dipstick marked in cm in the working range of my brewing. I printed out a conversion table that makes it easy to get an accurate volume very quickly from the dipstick.

How would you take into account diptubes, welded couples, mounted thermometers, or ribs in converted kegs?

[wahoo]

@Conroe

You can also just weigh it. A pint’s a pound.

1.04 lbs, exactly.

[bd1000]

[quote=“raspsu1”]I’ve tried the cm^3 to ml calculation on several of my brew items and it just doesn’t work out. I’m off by around a cm on each item. So let me see if I’m doing this correctly.

I’ve taken a pot that is marked in quarts. The Diameter of the pot is 30.5 cm, so that makes the radius 15.25 cm.

So using the forumula pi*(r^2)*h, that would mean each centimeter of height would be around 730 ml or around .77 quarts (I’ve rounded these numbers).

Its easier to read the quarts toward the top of the pot. If I measure where the 16 quart line is, it is around 19.75 cm. However, using the formula above, I’d need to be closer to 20.75 to get 16 quarts.

The error is even worse on my cooler.

Hmmmmm…[/quote]
You didn’t describe the shape of your pot or cooler exactly. Even if it were cylindrical with a consistent cross section, you’d at least have a small radius on the bottom and whatever valve/bulkhead fitting taking up some volume. Personally, I’d use some known-volume water jugs to mark your dip stick and stick with that.

[raspsu1]

[quote=“bd1000”][quote=“raspsu1”]I’ve tried the cm^3 to ml calculation on several of my brew items and it just doesn’t work out. I’m off by around a cm on each item. So let me see if I’m doing this correctly.

I’ve taken a pot that is marked in quarts. The Diameter of the pot is 30.5 cm, so that makes the radius 15.25 cm.

So using the forumula pi*(r^2)*h, that would mean each centimeter of height would be around 730 ml or around .77 quarts (I’ve rounded these numbers).

Its easier to read the quarts toward the top of the pot. If I measure where the 16 quart line is, it is around 19.75 cm. However, using the formula above, I’d need to be closer to 20.75 to get 16 quarts.

The error is even worse on my cooler.

Hmmmmm…[/quote]
You didn’t describe the shape of your pot or cooler exactly. Even if it were cylindrical with a consistent cross section, you’d at least have a small radius on the bottom and whatever valve/bulkhead fitting taking up some volume. Personally, I’d use some known-volume water jugs to mark your dip stick and stick with that.[/quote]

That’s the issue i was finding last night. So I may just need to pick one container with markings, use that for my standard measurement and figure out all my volumes standardized to that.

[a10t2]

@Wahoo

[quote=“Conroe”]You can also just weigh it. A pint’s a pound.

1.04 lbs, exactly.[/quote]
Depending on temperature, and how you define the pint and the pound.

I <3 the metric system.

[slothrob]

[quote=“raspsu1”]If I measure where the 16 quart line is, it is around 19.75 cm. However, using the formula above, I’d need to be closer to 20.75 to get 16 quarts.

The error is even worse on my cooler.

Hmmmmm…[/quote]
I think what you have discovered is the problem with pre-existing marks on containers, in general. The radius-to-volume measurement, if done carefully, is accurate, while the markings on large containers is often crude, at best.

@Baritone Brewer

How would you take into account diptubes, welded couples, mounted thermometers, or ribs in converted kegs?

Many of those take up so little volume as to be ignored, maybe a few mL each. If you really wanted to, you could calculate them once and just come up with a number that you add or subtract from your volume each time. The ribs are more of a pain. I use kettles, which are nice perfect cylinders, so it works well.

@bd1000

Personally, I’d use some known-volume water jugs to mark your dip stick and stick with that.

That works fine. It’s just a preference. After having done that once, years ago, I’ve found that 5 minutes with a ruler and a little math was easier and more accurate than 20 minutes fussing with a large, difficult to read measuring cup at the sink.

[a10t2]

@raspsu1

Its easier to read the quarts toward the top of the pot. If I measure where the 16 quart line is, it is around 19.75 cm. However, using the formula above, I’d need to be closer to 20.75 to get 16 quarts.

What temperature is the water? There’s a 4% difference between minimum and maximum density (at sea level). Are you sure the pot’s a perfect cylinder? If the radius is 15.2 cm at the base but 16.0 cm at the top, that would do it. For that matter, even if it is a perfect cylinder, the radius would only have to be 15.6 cm for the height to be 19.75. What’s the error bar on your measurements?

If you’re talking about the pre-drawn lines from the manufacturer, though, I don’t think you need to look any further for the source of error. They simply can’t be assumed to be accurate IME.

[raspsu1]

@a10t2

What temperature is the water? There’s a 4% difference between minimum and maximum density (at sea level). Are you sure the pot’s a perfect cylinder? If the radius is 15.2 cm at the base but 16.0 cm at the top, that would do it. For that matter, even if it is a perfect cylinder, the radius would only have to be 15.6 cm for the height to be 19.75. What’s the error bar on your measurements?

Well the thing that got me thinking of all this was that I took water from the tap to heat up for mash. When I put it the cooler, the volume was less by as much as a few cups which seemed werid since you’d think that with heating it up from faucet to mash temp that it would expand.

The other issue I’m having with the cm3 conversion is like you said, the pots seem to be slightly smaller on the bottom and then bigger at the top. Even if visually they look like a perfect cylinder, they are not. So that makes that very tough to calculate too.

I’m really enjoying this discussion. I like the critical thinking and math hehe.

[legman]

[quote=“Baratone Brewer”]Aluminum flat bar that I marked by filling my keggles a gallon at a time. I trust the ones that I marked.[/quote] Yep, made my own from a flat bar too. I marked it with quart increments.
It just clips to the edge of my kettle and since both of my kettles are the same, I just move it from one to the other.