Marvel Comics characters are notoriously difficult to properly scale, due to the constant staggering inconsistencies of the franchise.
In one moment Thor is capable of preventing the destruction of 1/5th of the universe, and in another he is knocked out by a shot from an ordinary handgun.
In some storylines the Hulk creates an earthquake reaching an infinite number of planets, or had his power level measured as infinite by the Pre-Retcon Beyonder, and in others he has been strangled unconscious by an ordinary python, or had serious trouble with regular gorillas.
This tendency is not at all limited to differences in opinions between different writers. For example, the Jane Foster version of Thor fought Odin (who has destroyed galaxies) in one comicbook, just to be manhandled by the Silver Samurai a few issues later by the same author.
Most Marvel stories are basically built on these types of massive plot induced stupidity inconsistencies, and it is blatantly obvious that most of the writers do not care about maintaining anything remotely resembling coherent logic regarding the relative power levels of different characters.
And that is likely fine for most readers, but it leaves the task of accurately scaling the characters nearly impossible.
In lack of better options, we decided to use the Marvel handbook statistics for the characters, since, given the above, that is virtually the only way to know how powerful that the characters are officially supposed to be in relation to each other.
Of course, there are various problems with this approach, not the least of which being that characters in the same strength or speed tiers usually have wildly different degrees of feats.
...And so onwards. So we are well aware of most of the problems with this system, but it still seemed to be our least bad option.
Anyway, regarding the specifics for the scaling:
We mainly use a combination of the statistics from the "Master Edition" handbook (Available here), and the current version (Seen in the respective character profiles of the Marvel wiki).
The modern version of the handbook is more up to date, and as such generally holds priority if the statistics conflict with each other.
However, the speed statistics within it are far less precise for lower levels. What rated as "Normal", "Athlete", "Peak Human", and "Enhanced Human" speed in the Master Edition, are all baked into speed level 2 in the new handbook.
Also, unlike the previous handbook, it makes no distinction between flying speed and movement speed, despite that Marvel's executive editor, manager of its continuity, and writer of the handbook statistics, Tom Brevoort, has explicitly stated that it still very much exists.
This makes it hard to gauge the regular speed of characters that are able to fly.
In addition, strength tier 4 goes from "800 pounds" (Captain America's level) to "Class 25" (Possibly similar to Luke Cage, but this is unconfirmed).
Hence, we tend to prefer to scale from the Master Edition for these levels, unless a character has been visibly upgraded.
Take note that this is all still an imperfect work in progress, with several gaps, given that there are various levels that we do not have anything proper to scale from yet.
Below Normal (Master Edition) | Level 1 (Current Handbook): Unknown
Normal (Master Edition) | Level 2 (Current Handbook): Unknown
Peak Human (Master Edition) | Level 3 (Current Handbook): At least Wall level+ (Scaling from Captain America)
Enhanced Human (Master Edition) | Level 4 (Current Handbook): At least Wall level+
Class 10 (Master Edition) | Level 4 (Current Handbook): Large Building level+ (Scaling from Spider-Man)
Class 25 (Master Edition) | Level 4 (Current Handbook): At least Large Building level+
Class 50 (Master Edition) | Level 5 (Current Handbook): City level (Scaling from base form Carol Danvers)
Class 75 (Master Edition) | Level 5 (Current Handbook): Large Mountain level (Scaling from an Iron Man feat, performed in an old armor listed as class 70)
Class 90: (Master Edition) | Level 6 (Current Handbook): Large Island level (Scaling from an Iron Man feat, performed in an old armor listed as class 85)
Class 100 (Master Edition) | Level 6 (Current Handbook): Multi-Continent level (Scaling from yet another Iron Man feat, performed in a newer armor that is estimated to be of this level)
Incalculable (Master Edition) | Level 7 (Current Handbook): Dwarf Star level (Scaling from Red She-Hulk)
Take note that the last category incorporates characters that have demonstrated far greater feats than Red She-Hulk. We simply scale from her, as a minimum, because she is supposed to be barely above the limit.
However, we also use consistency, and individual feats.
Also take note that we obviously definitely do not take the specific weight levels in the handbook seriously. We strictly use them for power-scaling purposes between different characters.
Below Normal (Master Edition) | Level 1 (Current Handbook): Unknown
Normal (Master Edition) | Level 2 (Current Handbook): At least Subsonic (Scaling from Mister Fantastic)
Athlete (Master Edition) | Level 2 (Current Handbook): Supersonic+ (Scaling from Hawkeye)
Peak Human (Master Edition) | Level 2 (Current Handbook): Hypersonic+ (Scaling from the Black Panther)
Enhanced Human (Master Edition) | Level 2 (Current Handbook): At least Hypersonic+
Superhuman (Master Edition) | Level 3 (Current Handbook): Massively Hypersonic (Scaling from Spider-Man)
Subsonic (Master Edition) | Level 3 (Current Handbook): At least Massively Hypersonic
Speed of sound (Master Edition) | Level 4 (Current Handbook): Defined depending on individual feats (In lack of better available options)
Supersonic (Master Edition) | Level 5 (Current Handbook): Faster Than Light (Scaled from Quicksilver)
Orbital velocity (Master Edition) | Level 5 (Current Handbook): At least Faster Than Light
Speed of light (Not available for regular movement in the Master Edition) | Level 6 (Current Handbook): Defined depending on individual feats
Warp speed (Not available for regular movement in the Master Edition) | Level 7 (Current Handbook): Defined depending on individual feats, but always Massively Faster Than Light+
However, take note that, due to extreme contradictions with the handbook statistics, we make an exception for high-tier characters that can be scaled from Thor.
Naturally, like everything related to Marvel statistics, this is very far from a perfect solution.
Marvel technically draws a clear distinction between durability and attack potency as well, but given that said durability scale is far less precise, mixes regerative ability with durability, and given that a character must logically be able to withstand the energy exerted by the body, we usually tend to rate this in proportion to the strength scale.
The most recent version of the handbook also ranks characters by their energy projection in a scale from 1 to 7. However, this is not useful for evaluating their statistics, as it strictly measures their versatility, not their scale of raw power.