Measuring Your Horse for the Correct Bit Size

Selecting the right bit size is as important as choosing the right type of bit. A correctly sized bit ensures comfort, clear communication, and prevents mouth injuries. Measuring accurately is the foundation of this process, and there are few different methods to achieve it.

Why bit sizing matters

Comfort: A bit that is too small pinches lips and cheeks; too large slides excessively and causes instability.
Clarity: Proper sizing allows the bit to sit evenly across the bars and tongue, transmitting aids without distortion.
Safety: Ill‑fitted bits can create sores, bruising, or encourage evasions like tongue retraction or head tossing.

Step‑by‑step methods for measuring

Using a hardwood dowel

Choose the dowel: Smooth, round, about 1.5 cm thick, longer than the horse’s mouth.
Placement: Insert gently into the mouth at the level where the bit would sit.
Marking: With the dowel centered, mark each side at the outer lip corners.
Measurement: Remove and measure the distance between marks with a ruler or tape.

You can also use a specially made bit measure tool, if you have a professional assessment the fitter will usually bring one.

Differences in sizing by cheekpiece style

Loose ring bits:

Require slightly more length (about 5 mm extra each side).
Rings move freely, so extra width reduces pinching of lips.
Example: If the mouth measures 135 mm, a 140 mm loose ring may be appropriate.

Eggbutt bits:

More stable, fixed cheeks.
Do not need extra width; size should match the mouth measurement closely.
Example: A 135 mm mouth measurement usually fits a 135 mm eggbutt.

Mouthpiece style and its effect on fit

Jointed bits (single or double):

Collapse in the mouth, and so can be considerably longer than the measurement but still appear to fit well from the outside..
This means many horses are ridden in jointed bits that are too long without riders being aware.
Double‑jointed designs distribute pressure more evenly, but still need careful sizing, and collapse in a similar fashion, but often to a lesser degree.

Solid bits (mullen, straight bar, ported):

Do not collapse, so they maintain full width.
Can be fitted closer to the exact mouth measurement.
Too much extra length causes sliding and uneven pressure.

Practical tips for accurate fitting

Check symmetry: The bit should protrude evenly on both sides, about 2–5 mm beyond the lips, depending on cheekpiece style.
Observe movement: Loose rings should slide without trapping skin; eggbutts should sit flush without meaningful gaps.
Test under rein: Apply light pressure; ensure no pinching or excessive sliding occurs.
Re‑measure periodically: Young horses’ mouths change with age; adults may need re‑checks after dental work.

Putting it all together

Measure carefully to establish mouth width.
Adjust for cheekpiece style: add allowance for loose rings, fit more exact for eggbutts.
Consider mouthpiece type: jointed bits may accommodate slight extra width; solid bits fit closer.
Confirm fit in practice: check for pinching, sliding, or uneven pressure during work.

Final note

Accurate measurement prevents discomfort and resistance, ensuring your horse can respond calmly and clearly to rein aids. Whether you use calipers, dowels or a proper bit measure, the key is consistency and attention to detail. A well‑fitted bit is a cornerstone of good horsemanship.