When i started making bonnets, i measured about 30 horses to get a general census on sizes. I made three categories, Cob/Lg Pony, Horse, and Oversize.
Cob/Lg Pony – Most large to medium ponies, arabians, small quarter horses
Horse – Most thoroughbreds, quarter horses, small warmbloods
Oversize – Warmbloods, draft crosses, small drafts
Ive found most horses fit in these categories, but with the occasional oddball. My gelding has tiny ears on a normal horse sized head. I make his bonnets in a horse size, but with cob sized ears. I made a custom bonnet for a small pony with horse sized ears (6″ !) If you think your horse has smaller or larger ears then the average horse, then follow the steps below for measuring.
The most important measurement is the ear length. The yarn has a good bit of stretch and give but the cotton fabric used for most of the ear coverings is not so accommodating.
So to measure the ears :
The average, that i have found :
Cob/ Lg Pony – 5.5 inches
Horse – 6 inches
Oversize -7 inches
I cut the fabric for the ear coverings to accommodate these measurements. The finished ear covering with have an additional quarter to a half inch on the measurements listed above, for comfort and accommodating. So if your horse is a smidge over 6″, it should still fit.
The following measurements are important for ordering custom show bonnets, or ordering a bonnet for a mini horse, small pony or larger draft.
And finally, measure the length of the forehead and where you would like the bonnet to end. Start at the poll, in between the two ears, and measure down to the forehead.