May only account for physical strength and not other abilities.
Suppression of power may lead to miscalculations.
May only be able to read to a certain limit before overloading.
May have limited range, including touch only.
Five Regents (Breath of Fire: Dragon Quarter)
Captain Comet (DC Comics)
Diana Ladris (Gone)
Users of Ki Sense (Dragon Ball)
Experienced Nen Users (Hunter X Hunter)
Naruto Uzumaki (Naruto); via Sage Mode
Gowther (Nanatsu no Taizai)
Merlin (Nanatsu no Taizai)
Users of Observation Haki (One Piece)
Fukuro (One Piece)
Boros (One-Punch Man)
Fuuka Yamagishi (Persona 3)
Rise Kujikawa (Persona 4)
Gyokuro Shuzen (Rosario + Vampire)
Force Users (Star Wars)
Satsuki (Starbiter Satsuki)
Milim (Tensei shitara Slime Datta Ken)
Ability Gauging Vendor (UnOrdinary)
Scouters (Dragon Ball series)
Energy Meter (Dragon Ball Z)
Scout-Scope (Dragon Ball Super)
Magic Power Finder (Fairy Tail)
Boosted Gear (High School DxD)
Ranking Scrolls (Moon-led Journey Across Another World)
Balor's Magical Eye (Nanatsu no Taizai)
Okame-chan (One-Punch Man)
Captain Comet (DC Comics) can evaluate his opponents' power levels with his Sense of Strength.
A Scouter (Dragon Ball series) can detect and read an individual's power level.
Son Goku (Dragon Ball) using Ki Sense.
Karin (Naruto) is a sensor of such caliber that she can sense the level of chakra of her targets.
While using Sage Mode, Naruto Uzumaki (Naruto) can sense and gauge chakra levels.
Using Enemy Zero, Gyokuro Shuzen (Rosario + Vampire) can read any power and Yokai energy she scans with the eyes on her palms, right down to quality and quantity.
The Boosted Gear (High School DxD) can determine an opponent's power level and tell Issei when his boost has built up sufficient power to possibly defeat an opponent, either by utilizing it himself or transferring it to an ally.
Jaune Arc's scroll (RWBY) measures and displays the Aura levels of Team JNPR.
Qui-Gon Jinn (Star Wars) taking a blood sample from Anakin to measure his midichlorian count.
A Magic Power Finder (Fairy Tail) measures the power of a spell's strength when the spell makes contact with the item.
Milim's (Tensei shitara Slime Datta Ken) "Milim Eye" can gauge the strength/magicule levels of those she sees, and appears to work even if they're masking their strength/magicule levels.