Upvote:2
@LarsBosteen has already put together a very good estimate of numbers for White armies here.
The main thing I would emphasise in addition to that answer is that there were several allied (beyond the Allied troops in White service) armies which fought alongside the Whites: Finns, Baltic Landeswehr (which never really got round to fighting the Reds but that was the original intention), Latvians, and Estonians being the most considerable on the north-western front. While these would have fought in theory alongside the Whites, they wouldn't have been under White flags and their goals were very different though their enemy was the same.
The numbers for all of these units would have varied considerably from month to month so it becomes too broad to focus on this in general terms.
After conscription was introduced in May 1918, the army's numbers swelled considerably:
By November, ... 47 rifle divisions (116 brigades and 339 regiments), four cavalry divisons and one cavalry brigade had been formed. By the end of 1918 there were 12 field armies numbering more than 285,000 infantry and cavalry. ... by spring 1919 it [the Red Army] already numbered 1,630,000.
In December 1919 the Red Army numbered three million men; by 1 November 1920 this had increased to 5.5 million.
βKhvostov, 'The Russian Civil War (1)'