Leghorns are good layers of white eggs, laying an average of 280 per year and sometimes reaching 300–320. The eggs are white and weigh a minimum of 55 g.
In Italy, where the Livorno breed standard is recent, ten colour varieties are recognised. There is a separate Italian standard for the German Leghorn variety, the Italiana (German: Italiener).
The Fédération française des volailles (the French poultry federation) divides the breed into four types: the American white, the English white, the old type (golden-salmon) and the modern type, for which seventeen colour variants are listed for full-size birds, and fourteen for bantams; it also recognises an autosexing variety, the Cream Legbar. Both the American Poultry Association and the American Bantam Association (ABA) recognize a number of Leghorn varieties including white, red, black-tailed red, light brown, dark brown, black, buff, Columbian, buff Columbian, barred, and silver.
In Britain, the Leghorn Club recognises eighteen colours: golden duckwing, silver duckwing, partridge, brown, buff, exchequer, Columbian, pyle, white, black, blue, mottled, cuckoo, blue-red, lavender, red, crele and buff Columbian. Most Leghorns have single combs; rose combs are permitted in some countries, but not in Italy. The legs are bright yellow, and the ear-lobes white.
The Italian standard gives a weight range of 2.4–2.7 kg (5.3–6.0 lb) for cocks, 2.0–2.3 kg (4.4–5.1 lb) for hens. According to the British standard, fully grown Leghorn cocks weigh 3.4 kg (7.5 lb), hens 2.5 kg; cockerels weigh 2.7–2.95 kg and pullets 2–2.25 kg; for bantams the maximum weight is 1020 g for cocks and 910 g for hens. Ring size is 18 mm for cocks, 16 mm for hens.