The brush hole in the shaving brush is usually about 5/8 inches in diameter.
The loft of the brush is measured from the top of the handle to the tips of the bristles. The average knot size is around 20mm, but higher end brushes and those favored by shaving enthusiasts tend to be larger, upwards of 24-28mm.
How Are Shaving Knots Measured?
The height that the knot is set into the handle of the shaving brush is defined when we talk about loft in a shaving brush. The loft of the brush is measured from the top of the handle to the tips of the bristles. 
What Is Shaving Brush Knot Size?
The average knot size is around 20mm, but higher end brushes and those favored by shaving enthusiasts tend to be larger, upwards of 24-28mm. The length of the actual bristles is measured from the base of the knot to the tip of the hair. 
What Is The Loft Of A Shaving Brush?
The length of the knot is described by the loft. Longer lofts will give you more flexibility in the bristles, which can cause them to become floppy. A shorter loft will give more stability to the bristles. 
What Is The Knot Of A Shave Brush?
The top portion of the shaving brush is referred to as a knot. Knot comes in a variety of grades and attributes. The knot is measured at the base of the hair, where the fibers meet the handle. 
Frank Harmenstein is the lead editor of the grooming website Cut Throat Straight Razor, and has over 15 years of experience in the industry. He’s personally tested and reviewed over 200 different straight razors, and has written countless articles on the subject.