The Lost Cause spilled a lot of ink on their weakness in numbers (DH Hill summarised their arguments). Their numbers for the Peninsula Campaign and the Seven Days in particular are invariably their "effective strength" excluding officers and extra duty men. This will attempt to estimate Federal strength the same way as the Rebels got their 80-90,000 strength.
Taking the averages of several estimates of strength by the rebels they typically estimate their infantry at 75% of PFD, artillery at 90% of PFD and cavalry at 60% of PFD. These numbers are applied here to the Federals.
2a. Infantry Effectives
To determine infantry effectives first the 20th June 1862 return is taken and the number of enlisted PFD for each division is taken. This is converted to PFD on 26th by the methodology of Burton (-2.5% or -0.5% per day). The attached artillery is deducted at 20 men per gun to yield the number of enlisted infantrymen for duty on the 26th June. The number of "extra duty" men is estimated at 25% of PFD and thus deducted, yielding ca. 63,000 "effectives" (table 1).
Taking other measures give slightly larger numbers. Including officers (rather than adding separately as in 2d) would give ca. 66,000, and decreasing the extra duty to 20% gives ca. 67,300 without officers (70,500 with).
Table 1: Number of Effective Infantry Present on 26th June 1862 (Click to Expand)
It is assumed that the artillery has only 10% extra duty men.
Table 2: Number of Artillery Effectives on 26th June 1862
2c. Cavalry Effectives
The cavalry has a larger extra duty element than the infantry, and effectives are rated at 60% of PFD.
Table 3: Number of Cavalry Effectives on 26th June 1862
2d. Total Effectives
The result of tables 1-3 plus officers (at 97.5% of PFD on 20th June) is summarised in table 4.
Table 4: Number of Effectives on 26th June, Officers Added