How to Measure for a Horse Bit

Whichever type of bit you choose for your horse, it should fit just right. Bits come in standard sizes, which typically makes it easy to take your horse's measurements to the store and come home with the right bit. The way your horse's mouth is shaped sometimes can change how a standard bit fits, but in general, measuring a horse's mouth is a good starting point to find a well-fitting bit.

How a Horse Bit Should Fit

It can take a good amount of adjustment to correctly fit your horse's bit. A bit that is too large will move back and forth in the horse's mouth and could possibly damage its teeth. And a bit that is too small can result in pinching and rubbing and make it difficult for the horse to properly close its mouth.

A bit should extend approximately a quarter-inch (0.6 centimeters) beyond the horse’s lips on either side, and it should fit comfortably across the bars (the toothless gap between the incisors and molars) of the horse’s jaw. If your horse is chewing the bit, tossing its head, or otherwise acting uncomfortable, there's a good chance the bit isn't positioned correctly. Lift the horse's lips to check the fit and adjust accordingly.

Measuring for Bit Fit

There are a few standard ways to measure the correct width of a horse's bit.

• Measure an old bit you already know fits from the inside of each cheek piece or ring. This will be your guide for the new bit. If you've just acquired the horse, try asking the previous owner for the measurement and type of bit they were using. 
• Cut a piece of string about a foot (30 centimeters) long, and tie a knot about 2 inches (5 centimeters) in. Pull the string through your horse’s mouth with the knot against its lips on one side. Mark where the string hits the other side of its lips with a marker or small piece of tape, and measure the span between the knot and your marker. A small wooden dowel can be used in place of the string.
• Pull a sewing tape measure (the flexible cloth or plastic kind) through your horse’s mouth, and measure the distance between the lips. 
• Use calipers. Adjust each arm of the caliper on either side of the horse’s mouth, and measure the distance between the two arms. Buying a pair of calipers for a one-time measuring job is expensive, so do this only if you already have a device available.

When you go to buy a bit, bring your horse's measurement and a tape measure to verify the bit's size. At the store, ask whether the bit can be returned if it doesn’t fit. Depending on the horse, you might have to try several bits before landing on the right one, so if possible, shop at a store with a good return and exchange policy.