The new Ukrainian brigades have about 2000 men according to David Axe, including the 47th, the 82nd, the 22nd for instance etc. That is the size of a Russian regiment (or a brigade of theirs - there is no substantial difference). Certain Russian brigades such as naval infantry or mountain ones before the war had around 1500 men. Russia as far as I read is beginning to include a fourth motorized battalion in part of its brigades/regiments though, plus Storm Z units.

The Ukrainian brigades that existed before 2022 were definitely larger as in addition to the standard 3 mechanized battalions + 1 tank battalion scheme, they often included 1 or even 2 motorized battalions, generally volunteer units formed during the 2014/15 conflict that were then institutionalized and put under the command of a regular formation.