Meganium
Meganium is almost exactly the height of Dragalge.
POKÉMON · HEIGHT & WEIGHT
Dragalge is 1.8 m (5 ft 11 in) tall and weighs 81.5 kg (180 lb).

Pokémon names and artwork © Nintendo, Creatures Inc. and GAME FREAK inc. Size It Up is an unofficial fan project and is not affiliated with or endorsed by them. Image source ↗
An average adult stands about 175 cm, so Dragalge is 1× as tall as a grown-up.
Of the 127 Pokémon entries measured on this site, Dragalge ranks 17th by height.
Meganium is almost exactly the height of Dragalge.
Kingdra is almost exactly the height of Dragalge.
Furret is almost exactly the height of Dragalge.
This page.
Crobat is almost exactly the height of Dragalge.
Typhlosion is a little shorter than Dragalge.
Skarmory is a little shorter than Dragalge.
See all 127 Pokémon sizes, smallest to largest
Numbers are easy to read and hard to picture. In Size It Up you drag a mystery object until it looks right next to a reference drawn at true scale, then the reveal shows how close you came. Dragalge turns up in the daily puzzle at random, and the Pokémon practice set deals five Pokémon at a time.
Measurements are the canon figures listed on the Pokémon Wiki (Fandom) page for Dragalge ↗. Where a character has several forms, the size above is for the form shown in the artwork.