Different grower brands have different protein percentages. If you have a range in mind, look up what's available in your area, and choose the one that's closest, otherwise, if you're concerned, just keep them on chick starter until they are laying, and they'll be fine. If they're outside foraging, they should be able to get enough protein from the bugs and worms they get out there, so they'll be fine.
Edit to add: Unless they love the mash, you can find crumble or pellet in any of the feed you get for them. I find mash gets wasted a lot, but that could be just me.
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Starter or grower should be fine. Hold off on the layer until they start laying.