Horse bit fitting guide

Choosing the correct size of bit for your horse


 Bit size considerations:

  •  The width of your horses mouth.
  • The thickness of your horses lips.
  • The side of your horses tongue.
  • The mouthpiece of bit selected.
  • The bit ring style you have chosen.


With so many different types of bit on the market, it can often be a minefield trying to choose which one. But more importantly you need to choose a bit that is correctly fitting and comfortable for your horse. As with all elements of a horse, the anatomy of a horse’s mouth can vary widely from one horse to another. If the bit is too tight it can cause pain, pinching, and generally distrust in the riders hands when ridden. Equally using a bit that is too loose can cause just as much trauma as it is likely to move around causing damage to the teeth, tongue and the palette. Sometimes people choose a bit that is wider for the horse, thinking that this is kinder. This is not the case and care must be made to select a bit of the correct width. It is not possible to give bit size estimations such as 4.5 inch for ponies etc, because horses and ponies of the same height may have widely varying mouth widths.

Your horses bit size may also vary depending on the bit type selected. Some mouthpieces are more curved than others and this may alter the size suitable for your horse.

 A horse wearing a snaffle bit and bridle, correctly fitted.


A starting point for bit measurement would be to analyse their current bit first. The horses bit needs to be at the correct height as this will affect the width in their mouth which narrows towards the front. The bit should be neatly fitting into the corners of the horses mouth, parallel to the second two grooves on the roof of the inside of his mouth. To judge the bit width most accurately this should be done with contact on the reins. With contact on the reins there should be an index finger’s clearance between the bit and the mouth. For loose rings, the horse’s lips should clear the bit ring holes by 1/8 inch on each side, to prevent pinching. If you can see half an inch or more, the bit is too big for the horse or pony.

To measure your current bit, you need a ruler. Lay the bit flat on a hard surface on top of the ruler. The length of the bit is the distance from the inside of one bit ring to the other. For a loose-ring bit, measure from the inside of the hole for the ring. Next you need to know the diameter of the horses bit. The diameter of the bit is measured at the widest part of the mouthpiece near the bit ring. As a general guide it is considered that the wider the mouthpiece the milder the bit as this gives more weight bearing surface across the bars. This would be more important for more novice riders that may not have balance and a consistent and sympathetic contact established.  Generally the thickness of the mouthpiece can vary from 12mm to 23mm. 12mm to 14mm would be considered a very fine mouthpiece, 16mm would probably be the most common size, and anything 20mm and above would be wide.

If you have no current bit to measure off, there are bit measuring devices on the market, but as this is likely to only get used once you can make a DIY one. You can make your DIY bit measuring device by using a section of wavin pipe placed gently at the correct height in the horses mouth, and use a marker on either side where the bit should ideally fit. There can be a bit of trial and error in getting the ideal bit for your horse, but it is vital that they are comfortable and happy when ridden.

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