Let's take a look at how big Kurama is using two different methods........
Method 1-Uses pixel scaling:
During the flashback of when Naruto was born in chapter 501, Kurama was unsealed from Kushina. Kushina was being held in chains attached to rocks. The black bit with wite pants in the picture is Kushina standing upright as seen in a later scan.
Now first thing to do is calculate the height of the rocks, since above those rocks is where Kurama is going to appear. To do this we use the relation of a standing Kushina in comparison to the height of the rocks to the complete left and right. Kushina measures 165 centimeters which is 32 pixels in the picture. Using the pixel-scaling program ImageJ to then measure the height of the rock on the right gives a height of 1603,594 centimeters. Doing the same measurement for the rock on the left gives a length of 1588,125 centimeters. This means that the average rock size is (1603,592+1588,125)/2 = 1595,8585 cm or roughly 15,96 meters.
Now that we have the size of the rocks, let's look at the panel where Kurama comes out of Kushina. You can see Kurama towering over the rocks.
Using this panel we can calculate the height of Kurama standing above those rocks. Using the same scaling idea, we'll now scale Kurama from those rocks (since Kushina is so small you can't scale directly from her). Using the average of 1595,80 centimeters for both, the scale was set at the right rock with it's height of 21 pixels measuring this. Measuring the left rock afterwards gave it a height of 1659,68 centimeters so as is visible there is some uncertainty in the scaling albeit it being below 10% of the actual value makes it acceptable. Now measuring from Kurama's teeth to the ground puts it's length (with the back legs partially stretched out) at 39002,57 centimers which due to the uncertainty we'll just round down to 390 meters.
Now given as we can see in the previous scans Kurama's tails are about the same length as his body. Due to this we'll could assume his tails are 390 meters in length. This is furthermore supported by the instance of Kurama charging a Bijuudama where his tails curl to in front of his mouth. However to make it more accurate we use the relation of tails to body length from 50% Kurama as seen in chapter 499 as despite being smaller it still has the same bodily proportions as Kurama.
Using the distance of the middle between the ears till the the line perpendicular to Kurama's body length which ends at Kurama's stretched-out leg as 390 meters since it most resembles Kurama's length and pose during the previous scan. This gives a value of Kurama's tail length of 535,93 meters, rounded down to 536 meters. This is of course with some inaccuracies in the order of 10s of meters due to the fact that the lengths have inaccuracies in measuring them, with as a result that the tail length may be shorter.
To get some insurance we use the scan in which we see a sealed Kurama to determine the tail's length since here Kurama is almost stretched flat.
Using the distance of the chains between the legs to the middle of Kurama's ears here in relation to the tail's length to determine the length of the tail gives a value of 439,75 meters till the curved bit of the tail. Given that this is almost all of Kurama's tail as seen in the scan this puts Kurama's tail length logically at a maximum of 536 meters and at minimum at 440 meters.
Now we try to get Kurama's height it's standing on all fours like it usually does. As can be seen throughout the series in numerous instances as when the fox attacked Konoha and the instance in which he first appears in a flashback to attack Konoha, one can see that the Kyuubi's lower arms make up almost the entire height of the Kyuubi.
Now using the same scan of the sealed Kurama used to calculate the tail's length to calculate the length of it's bottom arm (measured from the palm to the joint) we get a value of 103,77 meters. This means that Kurama stands just over 100 meters tall.
Now how credible is this calc?
As can be seen during the previously shown scans of the invasions of Konoha at chapter 1 and chapter 502, Kurama towers over the buildings and the large trees that the Narutoverse possesses (shinobi can freely jump through them and fall over 10 meters just falling off the branches on the side of the trunk). Furthermore it can be seen during the invasion scan that Kurama's head is roughly the size of a multi-story building and in the scans below that a horizontally fired off Bijuudama reaches the faces near the top of the hokage monument, on which we can see Minato standing and which Naruto at chapter 1 can be seen in relation to it as well.
This should give enough credibility to the calc due to the size of the hokage monument furthermore being comparable to modern-day flats in the distance as seen during the final chapter.
Original site: Here
Method 2- Scaling:
Kurama — The Nine Tailed Fox — Gamabunta is over 55 feet tall, but when Gamabunta is laying down his body is twice the length of his height, being at 110 feet long. Gamabunta was summoned when Kurama attacked Konoha, and when laying on top of Kurama covered about half of his torso. Meaning that Kurama's torso is about 220 feet long. Legs are twice as long as a person's torso, meaning that Kurama's legs are 440 feet long when he was at his full height. Kurama's neck and head are 1/5th the height of his torso, and over twice as long. That makes his head 44 feet tall, and 88 feet long. His ears are 1.5 times the length of his head, being 132 feet long. Kurama's tails are twice the length of his main body, from his nose to his rear end.220 + 440 + 88 is 748 and double that is 1496 feet long for the length of his tail. Kurama's ears are 132 feet, his head and neck are 44 feet, his torso is 220 feet, his legs are 440 feet. Kurama's height when standing, measuring from his ears to the ground, is 836 feet tall. Kurama at his full height is over 836 feet tall before his size was reduced.220 + 440 + 88 + 1496 = 2244 Kurama, from his snout to the tip of his tails is over 2244 feet long, before his size was reduced.
Kurama's Height: 836 Feet or 254.8 Meters... or 255 Meters when rounded up. Kurama's Length: 2244 Feet or 683.97 Meters... or 684 Meters when rounded up.
The Smallest Height for something to be considered a mountain is 1,000 Feet.
Which one of these methods is closer to the truth?