There are standardized, but very complex and somewhat difficult engineering methods, and there is also a simple rule which gives fine practical results for most purposes.
Greenhill's Rule dates from the blackpowder era, and states that "The twist in calibers times the bullet length in calibers equals 150."
Various folks have used different values for Greenhill's constant, but if you stick to the 150 value you will have a twist rate which is highly reliable for serious hunting or military use, which was the original intent, and the recommend twist will be amazingly consistent with those derived from good engineering practice with modern methods.
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