Houndoom
Houndoom is almost exactly the height of Ampharos.
POKÉMON · HEIGHT & WEIGHT
Ampharos is 1.4 m (4 ft 7 in) tall and weighs 61.5 kg (136 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 Ampharos is about 80% of the height of a grown-up.
Of the 127 Pokémon entries measured on this site, Ampharos ranks 36th by height.
Houndoom is almost exactly the height of Ampharos.
Hitmontop is almost exactly the height of Ampharos.
Granbull is almost exactly the height of Ampharos.
This page.
Wobbuffet is a little shorter than Ampharos.
Barbaracle is a little shorter than Ampharos.
Amaura is a little shorter than Ampharos.
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. Ampharos 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 Ampharos ↗. Where a character has several forms, the size above is for the form shown in the artwork.