Subject to HARMONISED EUROPEAN STANDARD ETSI EN 300 328 v2.1.1 (2016-11)

4.3.1.2.3 Limit

The maximum RF output power for adaptive Frequency Hopping equipment shall be equal to or less than 20 dBm.
The maximum RF output power for non-adaptive Frequency Hopping equipment shall be declared by the manufacturer.
See clause 5.4.1 m). The maximum RF output power for this equipment shall be equal to or less than the value declared by the manufacturer. This declared value shall be equal to or less than 20 dBm.

This limit shall apply for any combination of power level and intended antenna assembly.

Above extract from ETSI.ORG

Transmit power (Tx) has ± (plus /minus) 1dBm tolerance and is always lower towards the end of the allowed channel spectrum to minimize noise leakage to the next licensed channel spectrum.  

There have been occasions when it is mistakingly advertised as 26dBm or 400mW because such advertisements take into consideration the combination of the radio capability and antenna gain to inflate the total transmit power. This is incorrect.

---