How to measure the correct horse bit size
Bit size normally refers to the usable width of the mouthpiece between the cheekpieces. Measuring consistently makes it easier to compare models and avoid a bit that pinches or moves too far sideways.
Bit size conversion: millimetres and inches
Use the following common equestrian size equivalents when choosing a ByLynga bit.
| Millimetres | Inches |
|---|---|
| 95 mm | 3¾" |
| 105 mm | 4¼" |
| 115 mm | 4½" |
| 125 mm | 5" |
| 135 mm | 5¼" |
| 145 mm | 5¾" |
Method 1: measure a bit that already fits
- Place the clean bit on a flat surface.
- Measure the mouthpiece from the inside of one cheekpiece to the inside of the other.
- Record the result in millimetres.
- Note whether the bit has fixed or loose rings.
Method 2: use a measuring tool
Use a purpose-made bit measure or another safe, smooth measuring aid. Never use anything sharp or unsuitable in the horse’s mouth.
Fixed and loose rings
Loose-ring bits generally need enough clearance to move without pinching. Fixed rings normally sit closer to the mouth corners and provide more lateral stability. Do not apply the same allowance blindly to every design.
Common mistakes
- Measuring the total width including rings.
- Assuming every model fits identically in the same marked size.
- Ignoring mouthpiece thickness and shape.
- Changing size and construction at the same time without evaluation.
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Key points
- Start with oral health, anatomy and correct fit.
- Assess width, height, thickness, mouthpiece and cheekpieces as one system.
- Change only one important factor at a time where possible.
- Stop using the equipment if there are wounds, pain or clear distress.
How to evaluate in practice
- Record the current equipment and the horse’s response.
- Check teeth, oral tissues, bridle and bit.
- Test changes first in a calm, safe environment.
- Observe bridling, swallowing, contact, steering and behaviour.
- Check the corners of the mouth and oral tissues after riding.
Frequently asked questions
Is there one solution for every horse?
No. Oral anatomy, training, the rider’s hands and intended use vary. Individual fit is decisive.
How long should a change be tested?
If the horse is comfortable and safe, several short sessions provide better evidence than one trial. Stop immediately if pain or injury appears.
When is professional help needed?
Consult a veterinarian for wounds, swelling, sudden behavioural change or suspected dental problems.
Rules and safety
For competition, always check the latest rules of Horse Sport Ireland and the FEI TackApp where applicable. A product name alone does not prove eligibility.
General information does not replace an individual examination. Last fact-checked: 7 September 2026.