[ultravista]

Sure, you can't see how much is left, but after a few batches, you'll get the 'feel' by weight. Full, 3/4, 1/2, and near empty are (of course) much different.

By merely lifting the keg, you'll have a good understanding of what is left. Such as, this is going to blow after a few pints or damn, this keg is lasting a long time

[HoosierBrew]

Here's a low tech one - a dry erase board to mark each pint you pour. 40 pints/keg. The only drawback - non pint glasses. Still not hard to ballpark.

[jeffy]

A friend of mine uses a scale.  Weigh the keg empty first and then you'll know how much beer weight it has.
You can also take the keg out of the cooler and observe the condensation line as it warms.
I just lift mine gently and guesstimate the weight if I'm curious.

[Stevie]

The anxiety is peaked when trying to fill a growler when you know it's getting close.

[HoosierBrew]

The anxiety is peaked when trying to fill a growler when you know it's getting close.

Yeah, been there. You get it 3/4 full of clear beer, then the damn sediment blows in there. Expletives usually fly.

[brewinhard]

The anxiety is peaked when trying to fill a growler when you know it's getting close.

Yeah, been there. You get it 3/4 full of clear beer, then the damn sediment blows in there. Expletives usually fly.

Heh, heh...oh those are good times!

[Stevie]

The anxiety is peaked when trying to fill a growler when you know it's getting close.

Yeah, been there. You get it 3/4 full of clear beer, then the damn sediment blows in there. Expletives usually fly.

Or you aren't paying attention and blow a ton of gas in it causing a geyser of beer. I don't think I'm getting my security deposit back on the carpet.

[HoosierBrew]

The anxiety is peaked when trying to fill a growler when you know it's getting close.

Yeah, been there. You get it 3/4 full of clear beer, then the damn sediment blows in there. Expletives usually fly.

Or you aren't paying attention and blow a ton of gas in it causing a geyser of beer. I don't think I'm getting my security deposit back on the carpet.

Yeah, luckily it hits my garage floor. Doesn't make the growler full of cloudy beer seem any better, though.

[euge]

Leave the door open for a minute or two and condensation will tell you. I also rap a knuckle on the side of the keg and listen for the change in tone.

Lifting or tipping the keg can disturb any sediment in the bottom (shoulda used gelatin!) as I've found out to my dismay.

[HoosierBrew]

Leave the door open for a minute or two and condensation will tell you. I also rap a knuckle on the side of the keg and listen for the change in tone.

Lifting or tipping the keg can disturb any sediment in the bottom (shoulda used gelatin!) as I've found out to my dismay.

Yeah, I hear ya. Being a little less greedy and settling for the 3/4 full growler of clear beer wouldn't kill me, either.

[duboman]

I keep glassware on the top of my kegerator so its kind of a pain to open and check the kegs in any manner.

I'm usually the one doing most of the drinking so I have a general idea how long a keg will take to kick but its still sucks when you get that blast of gas and sediment on the last pull:)

[brewsumore]

Sometimes, when I tip a keg and see that it is very low, I'll bottle the remaining beer and put it in my beer fridge or cellar it, or to just have an alternative to what remains on tap, and/or to share with friends.  It also helps to get rid of the anxiety of "will I have room for the next two kegs almost due to fit in here?" 

I went on a fishing trip last weekend and before heading out had a low keg of Dubbel and was bottling other beers too to share with a fishing buddy from another state, and so bottled what I figured would be two or three beers left of the dubbel, but ended up bottling eight of them.  No big deal, I keep lots of empty bottles and caps on hand for just such situations.

[The Professor]

Rule #1: The beer in the keg will always achieve the perfect balance of flavor, carbonation, and clarity about 2 or 3 pints before it blows.    RDWHAHB and build up an inventory.

I learned that very thing 25 years ago and ramped up my brewing so that I now always have a few cornies on hand that have had at least 8 to 10 weeks of quiet  rest (and a lot longer for my IPA and Burton). 
A little diligence and a lot of patience result in tasty rewards.

[69franx]

Rule #1: The beer in the keg will always achieve the perfect balance of flavor, carbonation, and clarity about 2 or 3 pints before it blows.    RDWHAHB and build up an inventory.

I learned that very thing 25 years ago and ramped up my brewing so that I now always have a few cornies on hand that have had at least 8 to 10 weeks of quiet  rest (and a lot longer for my IPA and Burton). 
A little diligence and a lot of patience result in tasty rewards.

Professor, what does your IPA look like that you can age it that long? Lots of hops, or more English IPA style and traditional? Just curious, as most want to drink their AIPAs as fresh as possible. Just looking for new alternatives