How to Measure for a Bit
Here are some general guidelines for finding the correct size bit for your horse or pony. To shop our entire selection of English bits online, click
here. To find the right sized bit, you should consider both the length of the mouthpiece and the width of the mouthpiece in combination with the conformation of your horse’s mouth.
Eggbutt Bit | 
Double Jointed Loose Ring Bit | 
Hunter D Ring Bit | 
Full Cheek Bit | 
Elevator Bit | 
Kimberwicke Bit | 
Pelham Bit |
Length of the Mouthpiece The length of the bit corresponds to the width of your horse’s mouth. This measurement is usually provided in inches and fractions of an inch, such as 5" or 5 1⁄2".
When attached to an appropriately adjusted bridle, the bit should rest comfortably at the corners of your horse’s mouth. In general, the bit rings should not press very hard against the horse’s face, indicating that the length is too short. A bit that is too short may pinch the sensitive corners of the horse’s mouth.
A side view of the eggbutt snaffle bit. 
An eggbutt snaffle bit resting comfortably at the corners of the horse’s mouth. Conversely, if you see one-half inch or more of the mouthpiece on each side between the lips and the bit rings, the bit is too long. A bit that is too long can slip sideways in the horse’s mouth, becoming ineffective and causing soreness.
The specific type of bit you choose will slightly influence the desirable bit length. A
full cheek snaffle,
Pelham or
elevator bit should fit snugly next to the horse’s cheek, but should not squeeze or pinch.
For a
loose ring snaffle or any bit with moveable rings, make sure that the horse’s lips completely clear the bit ring holes by 1/8 inch on each side. Otherwise, the horse’s skin can become pinched into the holes as the action of the loose ring works with the rein.
The loose ring bit is sized so that the horse’s lip clears the hole where the loose ring slides to prevent pinching. Rubber bit guards can be used with loose ring bits to prevent pinching, but if you plan to compete with them, check with the governing body of your competition to be sure that their use is allowed. For example, bit guards are strictly forbidden in recognized dressage competitions and in dressage tests that are part of sanctioned and unsanctioned three-phase events. On the other hand, bit guards are allowed in show jumping classes.
You can measure your horse’s mouth to determine the length of bit required in two ways. The easiest way is to use a
Bit Sizer, which is a simple and inexpensive plastic measuring device that slides into the horse’s mouth. Inch increments correspond directly to bit sizes, and you take the reading just as you would using a ruler. As described previously, depending on the type of bit you’re selecting you may want to add 1⁄4 to 1⁄2 inch to the bit sizer measurement.
Using a bit sizer Alternatively, you can use a piece of string in place of a commercial bit sizer if your horse will cooperate. Mark the spots on the string that meet the corners of the horse’s mouth, then lay the string against a ruler to obtain your bit length measurement. Again consider the type of bit you’re selecting and whether you should add a bit of length to the measurement.
Width of a Mouthpiece 
The width of a bit refers to its circumference at the widest part of the mouthpiece. This measurement may be in either inches or in millimeters. For most horses, the thinner the bit, the more severe its action on the horse’s mouth. This is because the pressure from the bit is exerted on a narrower surface.
Similarly, in general, the thicker the bit, the more gentle its action on the horse’s mouth because the pressure is distributed over a wider surface. However, a qualification to this guideline is that the bit cannot be too thick in relation to the space in the horse’s mouth to accommodate it. The height of the palate (roof of the mouth) in combination with the thickness of the tongue determines the amount of space available for the bit. If the bit is too thick, it will put constant pressure on the horse’s mouth, and could even make swallowing difficult. Always consider the conformation of a horse’s mouth when choosing bit width.
Your equine dentist, veterinarian or a knowledgeable trainer can help you determine whether your horse’s palate is normal or high, which could allow for a thicker bit to be used, or very low, which could reduce the thickness of the bit that may be used. You can usually identify the conformation of the horse’s tongue by prying open the side of the lips. A small or average sized tongue lies below or level with the bars of the mouth. A thick tongue rises above the bars or spills over the bars and between the teeth.
Should I Borrow a Bit from a Friend? Borrowing a bit from a friend can be a useful tool for determining a type or size of bit to purchase. However, you should never put a used bit in your horse’s mouth without sterilizing it first.
The easiest way to sterilize a bit is to run it through a dishwasher cycle that supplies hot water at a 180 degree temperature.
Another method is to scrub all aspects of the bit with a soft toothbrush and a surgical scrub. Let the solution remain on the bit for 15 minutes, then rinse cleanly. Next, submerse the bit in a solution of one teaspoon bleach to one quart of water. Let the bit sit in the solution for 15 minutes, and then rinse it clean and dry thoroughly.
Note: Some bits made of combined metals, plastics, or rubber will discolor during sterilization.
