According to the standards of the Poultry Club of Great Britain, British Faverolles cocks weigh 4.08–4.98 kg (9–11 lb), cockerels 3.4–4.53 kg (7.5–10.0 lb), hens 3.4–4.3 kg (7.5–9.5 lb) and pullets 3.17–4.08 kg (7–9 lb); bantam cocks weigh 1130–1360 g and hens 907-1133 g. The Australian and United States standards call for a slightly smaller bird, but still a relatively large chicken. The Australian standard specifies that cocks weight from eight to ten pounds, hens six and a half to eight and a half pounds. The American Poultry Association standard is eight pounds for cocks, six pounds for hens.[1
They are a french breed breed for excellent breast meat, so they should have a very pronounced breast, eggs were seconday do medium to large is acceptable.
In the US we breed to characteristics not purpose, so many of our heritage breeds now are not good layers and lay medium to small eggs (Sicilian Buttercups are a good example of that ) . Several years ago the president of the Leghorn association wrote a very interesting paper on this topic.