Physical Dimensions & Thickness: The ASUS ROG Ally has a horizontal bar chassis measuring 280 × 113 × 39 mm, while the Valve Steam Deck uses a horizontal bar chassis measuring 298 × 117 × 49 mm. In width, the ASUS ROG Ally is 18 mm (6%) narrower than the Valve Steam Deck. In height, the ASUS ROG Ally is 4 mm (3.4%) shorter than the Valve Steam Deck. In chassis thickness (depth), the ASUS ROG Ally is 10 mm (20.4%) slimmer than the Valve Steam Deck (39 mm vs 49 mm).
Footprint Area & Weight: Calculating surface footprint (width × height), the ASUS ROG Ally occupies 31,640 mm² (316.4 cm²), compared to 34,866 mm² (348.7 cm²) for the Valve Steam Deck—a footprint difference of 3,226 mm² (9.3%). On the scale, the ASUS ROG Ally weighs 608g versus 674g for the Valve Steam Deck, representing a 66g (9.8%) weight difference (ASUS ROG Ally is lighter).
4:3 vs 16:9 Effective Viewable Screen Size: For classic 4:3 retro games (PS1, SNES, N64, Dreamcast), the ASUS ROG Ally's 7" (16:9) panel yields a 5.72" effective diagonal (75% active screen area with vertical pillarbox bars on the sides (native 16:9)), while the Valve Steam Deck's 7" (16:10) panel yields a 6.18" effective diagonal (83% active screen area with vertical pillarbox bars on the sides (native 16:10)). This gives the Valve Steam Deck a 0.46" larger active 4:3 diagonal (16.9% more active display area). For 16:9 widescreen content (PSP, Switch, streaming), the ASUS ROG Ally delivers a 7" effective diagonal (100% screen usage) versus 6.81" (90% screen usage) on the Valve Steam Deck, making the ASUS ROG Ally larger by 0.19" (+5.6% active 16:9 area).