This article assumes that you have taken measurements of your horse’s mouth and want to translate those measurements onto a horse bit, to enable you to find the correct size, or alternatively, you have an existing bit you already know fits your horse, that you can take measurements from.
We highly recommend using the services of a specialist bit fitter, to find a suitable bit for your horse, but if you want to do it yourself this is how to measure a horse bit using the correct measurements.
There are two important measurements taken from your horse’s mouth that are used when selecting a horse bit. They are the width side to side of your horse’s mouth and the size of the gap where the bit sits. For more information on how to take these measurements, read our article on “How to ensure a properly fitting bit”.
Whilst there are many variations, there are broadly three groups of bits that you need to know about in terms of measurements, Loose ring Cheeks, Fixed Cheeks, and Weymouth.
In addition to the ring being able to pivot forward and backward in the mouthpiece, as the name suggests, the rings on this bit can also slide through the mouthpiece providing ease of movement and motivating the horse to relax the jaw. The rings should be able to move freely, but there should be no more than a 5mm gap between the mouth and the bit rings. If the rings fit too closely, they can pinch the sides of the mouth and some horses may need a bit guard, a circular rubber disc shape that fits between the mouthpiece and the rings.
Make sure you lay your bit on a flat surface, stretching the rings apart so that the bit is straight. The width measurement of your horse’s mouth should correspond to the length measurement from the inside edge of the ring along the mouthpiece to the inside edge of the ring on the other side of the mouthpiece. (shown in the diagram below).
The size of the gap in your horse’s mouth should match the thickness or diameter of the mouthpiece. This measurement should be taken at the widest part of the mouthpiece, which is normally at the end just inside where the ring and the mouthpiece meet. You can take this measurement using a tape measure, but it is more accurate to use a bit measurer that normally includes a thickness gauge, or alternatively a set of callipers.
The diameter of the loose ring can be measured from top to bottom.
Bits that have fixed cheeks, such as the D-Ring or Eggbutt bit are fixed allowing the cheek ring to swivel forward and backward, but no upward or downward movement. Fixed cheek bits should sit as close as possible to the edge of each side of the mouth. For this reason, a fixed cheek bit should be one size smaller than a loose ring bit.
Laying the bit on a flat surface the mouthpiece width is measured from just inside both sides of the cheekpiece. The thickness measurement of the bit is taken from the end of the mouthpiece just inside the cheekpiece as shown in the image below.
The Weymouth bit is used as part of a double bridle and in tandem with a second bit called a bradoon. (don’t make the mistake of using a snaffle bit with a Weymouth bit as the thickness and size of the rings are normally too large, compared to a bradoon bit). Double bridles are used by experienced riders and for those competing in advanced dressage.
As well as the width and the thickness of the mouthpiece, there is an additional measurement required and that is the length of the lower shank. This is measured from the bottom end of the mouthpiece to the bottom of the shank. Weymouths are normally available in either 50mm or 70mm lower shank lengths.
The mouthpiece width measurement is taken in the same way as a fixed cheek bit and the thickness is measured at the thickest point where the mouthpiece fits into the shank.
The good news is that bits are sold in standard sizes and generally, bit measurements are illustrated in mm (millimetres), so if you have taken measurements in inches, you will need to convert them. Mouthpiece lengths vary from 95mm to 170mm, in 5mm increments. Recent research has shown that a horse’s oral cavity is actually smaller than originally thought. Most top brands offer thickness sizes between 12mm and 22mm with 14mm, 16mm, and 18mm being the most common sizes. Rings are available in sizes 55mm, 65mm, and 70mm.
When searching for a suitable bit for your horse, in addition to the width and thickness of the bit, you must decide whether you want a fixed ring, or a loose ring bit, whether you want the mouthpiece in a straight bar called a “Mullen Mouth”, or to be single-jointed, double-jointed, or even multi-jointed. Finally, there is a choice of materials that the mouthpiece is made from, such as rubber, plastic, copper, stainless steel, Aurigan, or Nickel plated.
The many different combinations of bit can seem overwhelming, however, most bit manufacturers also group bits by discipline, whether you are jumping, performing dressage, Eventing, or even just leisure riding and many also make specialist bits to help address specific concerns that a horse may be facing, such as excessive bit chewing, not taking the bit contact, putting the tongue over the bit, a sensitive mouth, or other behavioural issues.
Depending on your horse, you may need to try several different styles or shapes of horse bit until you find one that suits both you and your horse.