The Planck length is not observable but it is possibly the smallest "thing" in the known universe. Unless someday something smaller is found First we have to "find" something the size of the Planck length. We can't even see that yet so I reckon that it will be a while.

Planck length: 1.61619926×10^-35 meters which is 0.0000000000000000000000000000000000161619926 meters

The observable universe is arguably the largest "thing" we know of but I don't think anyone believes that it's the largest "thing". It's just the limit of our ability to record photons, for now.

The Observable Universe: 8.79829142×10^26 meters or 87,982,914,200,000,000,000,000,000,000,000,000 meters

I think the difference in scale is fascinating. As far as I know there is no frame of reference for this. I can't say "well, if the smallest "thing" as 1/4" diameter pea then the largest would be..." would be what? There is no way to reference the difference to anything that we see in our daily lives. The total difference (for now) is 10.4145 x 10^61 or 104,145 with 57 zeros after it. Try to imagine that. You can't. I don't even know what that number would be called. Maybe a gonzomegawowser? Actually... there is a number for it (yay internet). 10^62 power is one hundred novemdecillion (had to add that one to my spell check dictionary. I think I heard it choke)

Wouldn't it be interesting if we found out that the Universe was actually 1.61619926×10^35 meters "wide". Its only 9 orders of magnitude greater than what we know (or think we know). Then we could have a Kcnalp constant and all would be balanced.

Yup... that's the kind of thing that crosses my mind on a Friday night. When I party... I party hard...