Group size estimator

How many trainers do I need to invite?

The Estimator is already "trainers of this attacker needed to finish inside the timer", so this page does not invent a number: it reads it off the boss's own ranked counter list for three realistic parties and re-simulates each of them at every level from 20 to 50.

Raid bossTierIVsWeatherFriendshipDodgingShadow attackersMega attackersLegendary attackers

Invite 7 to be safe — 5 if everyone is prepared

At level 40, a party of Regirock's top six counters needs 4.71 trainers (round up: 5), and a mixed lobby of ranks 13-24 needs 6.18 (round up: 7). The raid timer is 300 seconds and one prepared trainer alone would take 22:15. No level in this range makes it soloable with a prepared party.

Regirock · Shadow Tier 5

rock

Weak to

fightinggroundsteelwatergrass

Boss CP: 42,768
Boss HP: 15,000
Raid timer: 300s
Party used: 6

Trainers needed, by attacker level

Scroll sideways for the mixed-lobby column.

Trainers needed to beat Regirock at each attacker level
Attacker level	Six of the best counter	A prepared party	A mixed local group	Prepared solo time	Faints per timer
Level 20	7(6.06)	8(7.49)	10(9.29)	35:21	6.0
Level 25	6(5.40)	7(6.23)	9(8.10)	29:26	6.0
Level 30	5(4.43)	6(5.10)	8(7.10)	24:06	5.9
Level 35	5(4.29)	5(4.89)	7(6.56)	23:06	5.9
Level 40	5(4.05)	5(4.71)	7(6.18)	22:15	5.9
Level 45	4(3.92)	5(4.57)	6(5.94)	21:34	5.9
Level 50	4(3.89)	5(4.46)	6(5.77)	21:04	5.9

Whole trainers in bold, the raw estimator in brackets — 2.04 means two trainers is right on the line and three is comfortable.

Six of the best counter

Every trainer brings six copies of the single best counter — the theoretical floor.

5 trainers at level 40

Zacian (Crowned Sword)4.05

A prepared party

Each trainer brings the boss's top six counters, powered up and correctly TM'd.

5 trainers at level 40

Zacian (Crowned Sword)4.05
Zamazenta (Crowned Shield)4.16
Necrozma (Dusk Mane)4.39
Keldeo4.53
Terrakion5.39
Blaziken5.76

A mixed local group

Ranks 13-24: reasonable but unoptimised parties, which is what a public lobby usually is.

7 trainers at level 40

Landorus (Therian)5.91
Eternatus5.99
Xurkitree6.07
Zarude6.10
Quaquaval6.13
Hisuian Decidueye6.13

The party these numbers assume

1. Zacian (Crowned Sword)

Metal Claw + Behemoth Blade

2. Zamazenta (Crowned Shield)

Metal Claw + Behemoth Bash

3. Necrozma (Dusk Mane)

Psycho Cut + Sunsteel Strike

4. Keldeo

Low Kick + Secret Sword

5. Terrakion

Double Kick + Sacred Sword

6. Blaziken

Counter + Aura Sphere

See the full ranked counter list for Regirock · check a real lobby (win chance, who brings what) · make a share card of the top six

How this is worked out

The boss is ranked once at level 40 with rankCached (the same memoised call /raids makes), then the three bands — rank 1, ranks 1-6, ranks 13-24 — are re-simulated at each attacker level with an 8-run Monte Carlo each. Holding the party fixed and moving only its level is deliberate: it answers "what if my party were level 20" rather than "what would a level-20 player's completely different party be", and it is about ten times cheaper than re-ranking every attacker seven times. The Estimator itself is Pokebattler's definition, time to win including rejoin time divided by the raid timer.