How big is Akamaru?

Answer 1

He just grew up like everyone else in Naruto Shippuuden albeit disproportionally as he suddenly doubled in size over two years after not changing at all throughout the first part of the series.

Answer 2

Vertically he's 2.9 meters from head to toe, ~2.5 meters shoulder to toe. an interesting point here is that he was 29 cm head to toe when he's small-before shippudden-.

Horizontally he's 4 meters from front to back with tail stretched.

so, quite a big dog.

foe how I calculated;

I used this image

http://cdn.okiah.com/wp-content/uploads/2010/07/Kibas-long-day.jpg

of Naruto Episode 184, Aakamru and Kiba are standing next to each other, so I used him as a reference, and Kiba's height at the time is around 152.5 cm.

in that image he's about 4.3 cm's tall, so 152.5/4.3 = 35 .465, the rest follows.

Answer 3

about 3 feet if he's on all fours.