Usually, the manufacturer will supply that in tech specs of the devices you are using, some you may have to hunt around for on the internet.
32 mW or 15dBm is what most laptops are doing, 13dBm is common for tablets, and around 11dBm for Smartphones. Our Balanced power setting on the ap's (found in AP properties) will deploy 13dBm on the radios for you by default.
Doug Hyde
Director, Technical Support / Extreme Networks