Power levels
HIGH SCHOOL DXD
Categories
The numbers represent Mana.
Tier 10: 0
Regular humans, animals, and other creatures with absolutely no magical power.
Tier 9: 1-99
Anyone from the weakest magic user (including but not limited to Issei when he was initially revived) to just below the average low-class devil. Can also apply to sorcerers who've just started their training.
Tier 8: 100-199
The varying power degrees of a normal low-class sorcerer, devil, angel, fallen angel, etc. Also applies to most magical creatures.
Tier 7: 200-299
The stage between low and middle class.
Tier 6: 300-399
Beings with middle-class magical power.
Tier 5; 400-499
The stage between middle and high class.
Tier 4: 500-999
High-class power.
Tier 3: 1,000-9,999
The stage between high and ultimate class.
Tier 2: 10,000-99,999
Ultimate-class.
Tier 1: 100,000-999,999
Satan/Seraph/Gov. General-like power. Examples: Serafall Leviathan, Azazel, Shimezhai, Michael the Archangel, Gabriel, Metatron. Zach Praktum (Balance Breaker).
Tier α: 1,000,000-9,999,999
Gods, Super Devils, certain monstrous gods, various Lovecraftian creations that might make appearances in the story much later on, and the Heavenly Dragons. Examples: the Abrahamic God, the original Satans, Rizevim Livan Lucifer, Sirzechs Lucifer, Ajuka Beelzebub, the Leviathan God, Ddraig, Albion.
Tier Ω: 10,000,000-∞ minus 1
The amount of power reserved for those who are above the normal gods and can bring about the end of the timeline. Examples: Ophis, Great Red, Trihexa, Gaia, Tartarus, Ouranos.
∞
Infinite power, only accessible to the three Primordial Ones. Anyone with this strength is absolutely impossible to overcome except by someone else with this power. The Only Three: Azrael (Lord of Balance), Satanael (Lord of Order), Kaira (Lady of Chaos).
CREATORS' THOUGHTS 
Ahmad_Kas
Ahmad_Kas from Dxd wiki
Weekly Power Status
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Ranking 
-- Power
stone