Did you ever pay attention to the “suggested group size” for raids? 5 for a Metapod, 9 for a Sandslash, 13 for a Machamp and 20 for a legendary.

Of course it doesn’t make sense.

Here I propose a (simple?) formula to calculate a much more realistic “suggested group size”.

Since there are different views on this topic, I provide three slightly different versions of the formula, only with different coefficients.

Hardcore players with extremely optimized attackers:

Minimum Group Size = ceiling [Defense x HP / Time / 3400] – 29% if double vulnerability

Typical L30+ players in a “regular” raid group with good L30 attackers:

Realistic Group Size = ceiling [Defense x HP / Time / 1700] – 15% if double vulnerability

Casual L20+ players who can do a Google search or ask more experienced players and just avoid basic mistakes like using Gyarados against Raikou:

Casual Group Size = ceiling [Defense x HP / Time / 1133] – 15% if double vulnerability

Defense x HP is just the raid boss’s tankiness.

Divided by time, it’s the needed DPS (Damage Per Second) to defeat the boss.

The coefficient is 3400 for the minimum group size (found heuristically as the best match with Pok√©battler simulations), then the group size is doubled for “regular players” (so 1700) and tripled for “casual players” (so 1133).

In case of double vulnerability, deduct 29% (i.e. full type effectiveness bonus) in case of “hardcore” minimum-group/solo raid, while only 15% (i.e. half of that) in case of “regular” or “casual” raid, because not everyone will have a full team of optimal doubly Super-Effective counters.

So here is the table for current raid bosses + Ho-Oh, sorted by increasing difficulty (which is just the “Realistic Group Size” with 1700 coefficient before the ceiling operation):

 Raid BossBase DEFHPVulnerabilityDifficulty (unrounded)Minimum Group SizeRealistic Group SizeCasual Group Size
Metapod94600single0.2111
Charmeleon129600single0.3111
Ivysaur151600single0.3111
Wartortle155600single0.3111
Sableye1411800single0.8112
Magneton1821800DOUBLE0.9112
Marowak2001800single1.2122
Sandslash2021800single1.2122
Porygon1393000single1.4123
Tentacruel2371800single1.4123
Scyther1703000DOUBLE1.4123
Gengar1563000single1.6123
Machamp1623000single1.6123
Omastar2273000DOUBLE1.9123
Cloyster3231800single1.9123
Alakazam1943000single1.9123
Ninetales2043000single2.0234
Victreebel1387500single3.5246
Nidoking1577500single3.9246
Nidoqueen1747500single4.4357
Entei18012500single4.5357
Lapras1807500single4.5357
Tyranitar2127500DOUBLE4.5257
Mewtwo18212500single4.5357
Poliwrath1877500single4.7358
Snorlax1907500single4.8358
Golem2297500DOUBLE4.9358
Raikou21012500single5.2368
Ho-Oh27412500DOUBLE5.8369
Suicune23512500single5.8369

An interactive calculator, also with legacy species, Mythical Pokémon and a field to calculate it for an arbitrary species / raid tier, is available as a spreadsheet.