Ork Rules Question: Grots & Herders

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I'm adding a unit of Grots to my messy Ork army, and I'm uncertain about the ratio of Grots to Herders. The rulebook says that it should be one herder to every 10 Grots, but I'm not sure what to do with the remainders. I know that if I have 25 Grots, I need at least two Herders (one for each full group of 10). Do I need a 3rd Herder for the remaining 5 Grots? Or do I only need a third Herder if I take 30 Grots?

[Nabterayl]

You need one runtherd for every full ten gretchin. Anything less than ten gretchin does not require a herder, so you could have, for instance, one runtherd and nineteen gretchin, or two runtherds and twenty-nine gretchin.

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Thanks Nabterayl!