Determining the correct horse bit sizing is crucial for your horse’s comfort and effective communication. The correct way to measure a horse bit involves checking the width across the mouthpiece, the length of the cheekpieces (or shanks for curb bits), and ensuring the bit’s action suits your horse’s mouth conformation.
Why Proper Bit Sizing Matters
A bit that is too wide or too narrow causes pain and misunderstanding. A bit that doesn’t fit well can pinch the corners of the mouth, rub the tongue, or sit too far back, making the reins feel ineffective. Getting the size right is the first step toward clear riding signals. It directly impacts your ability to succeed when determining correct bit size.
Part 1: Measuring the Width of the Mouthpiece
The most important measurement is the width across the bars of the bit. This measurement is usually what “bit size” refers to when you shop.
Tools Needed for Measurement
You will need simple tools for this task.
- A metal ruler or tape measure: Choose one that has clear, easy-to-read markings.
- A helper (optional but useful): Someone to keep the horse still while measuring.
Steps for Measuring an Existing Bit
If you have a bit that fits your horse well, use it as your guide.
- Lay the Bit Flat: Place the bit on a level surface.
- Measure Inside to Inside: Place your ruler across the bit. Measure from the inside edge of one mouthpiece (where it meets the ring or cheekpiece) to the inside edge of the other mouthpiece. This is the true measuring a horse bit mouth opening.
- Note the Unit: Record the measurement in inches or millimeters, depending on how bits are sold in your region. Most US bits use inches.
Steps for Measuring Your Horse’s Mouth (If Buying New)
Measuring the horse is more reliable than guessing based on breed.
- Use the ‘Finger Rule’ (Quick Check): Gently lift your horse’s upper lip. Place two fingers sideways between the corners of the mouth and the bars of the mouth (where the bit will sit). If you can fit two fingers snugly without too much squeezing, the mouth is likely average. This is a starting point, not the final measurement.
- Use the ‘Measuring Bit’: A better method uses a specialized measuring tool or a very thin, straight piece of wood (like a dowel) that is marked.
- Gently insert the dowel into the horse’s mouth where the bit would rest.
- Ensure the dowel is straight and touches the inside of the cheek on both sides.
- Mark where the wood touches the outside of the horse’s lips on each side.
- Take the dowel out and measure the distance between your two marks. This is the required bit width.
Standard Bit Widths and Adjustments
Most standard bits come in half-inch increments.
| Horse Size/Type | Common Bit Width (Inches) | Notes |
|---|---|---|
| Small Pony | 4.0″ – 4.5″ | Very small mouths require specific pony sizes. |
| Cob/Average Mare | 5.0″ – 5.25″ | Common range for many average-sized horses. |
| Average Horse | 5.25″ – 5.5″ | The most frequent size range found. |
| Large Horse/Draft | 5.5″ – 6.0″+ | Larger breeds often need wider mouthpieces. |
Crucial Tip: If your measurement falls between two sizes (e.g., 5.375 inches), most experts advise sizing up slightly if the horse has full lips, or sticking to the lower size if the horse has thin lips or fights a wide bit. A bit too wide will cause wrinkling at the corners of the mouth. A bit too narrow will pinch.
Part 2: Assessing Different Horse Bit Types and Their Fit
The way you measure and judge the fit changes depending on the different horse bit types you use. We look at snaffles, curb bits, and leverage bits separately.
Snaffle Bits (Direct Pressure Bits)
Snaffle bits, like the O-ring or D-ring, apply direct pressure. Fit is primarily about the width and the amount of ‘play’ in the mouthpiece.
The Mouthpiece Gap
When fitted correctly, a snaffle should sit evenly in the mouth. There should be slight wrinkles (one or two) at the corners of the mouth when the horse’s head is in a natural, relaxed position.
- If the bit is too wide, the rings will pull the corners of the mouth too far back, causing pinching.
- If the bit is too narrow, the center of the bit will push the corners of the mouth forward, creating excess bunched-up skin.
Curb Bits (Leverage Bits)
Curb bits use leverage applied via the shank, creating pressure on the poll, chin groove, and tongue. Sizing involves width and shank length measurement.
Measuring the Shank Length
The shank length dictates the severity of leverage.
- Position the Bit: Place the mouthpiece in the horse’s mouth as it should sit (see section above).
- Measure from Mouthpiece to Ring: Measure from the point where the mouthpiece meets the shank down to the bottom of the rein ring.
- Standard Ranges: Shank lengths vary greatly. Short shanks (3 to 5 inches) offer less leverage. Long shanks (7 inches and up) offer significantly more.
When measuring bit cheekpieces on a curb bit, remember that shank length directly influences the pressure applied when the reins are pulled. Too long a shank on a sensitive horse can result in accidental over-collection or harshness.
Pelham and Gag Bits
These bits combine features. Pelhams have shanks and often use a curb chain, requiring the same considerations as a curb bit, plus attention to the mouthpiece width. Gag bits rely on the sliding action along the cheekpiece to lift the head. Their width sizing remains the same as snaffles or curbs, but the action relies on the length of the cheekpiece shaft above the bit ring.
Part 3: Evaluating the Cheekpiece Length (For Curb Bits)
For any bit featuring shanks (curbs, pelhams), the cheekpiece length needs careful attention. This determines the angle and leverage.
How Cheekpiece Length Affects Action
The length of the side arm (shank) dictates how much downward pull on the rein translates into pressure under the chin via the curb chain.
- Shorter Shanks: Require more rein pressure to activate the curb action. Good for horses that need light refinement.
- Longer Shanks: Require less rein pressure to engage the curb, making the action quicker and potentially sharper. These are often used on experienced horses or those needing stronger signals.
When trying a new curb bit, start with a medium shank (around 5 inches) and adjust the curb chain adjustment before changing the bit itself.
Part 4: The Role of the Curb Chain Adjustment
The curb chain is vital for curb bits and pelhams. Incorrect adjustment makes even a perfectly sized bit feel wrong.
Correct Curb Chain Fitting
The chain sits in the chin groove, just behind the chin bone.
- Loosen the Chain: With the bit in the horse’s mouth and the reins held lightly (no pulling), the curb chain should hang loosely.
- Engage the Chain: Gently take up the slack in the reins until the chain makes light contact with the chin groove.
- Check the Gap: At this point, you should be able to slip one finger snugly between the chain and the chin groove. If you can fit two fingers, the chain is too loose, and the leverage will be delayed or ineffective. If you can only fit your index finger with difficulty, it is too tight, and pressure is constantly applied to the chin.
Horse bit gauges often don’t account for this adjustment, so it must be done on the horse. Correct curb chain adjustment ensures that the leverage engages only when you ask for it, not when the horse simply moves its head.
Part 5: Mouthpiece Material and Shape Considerations
While not strictly about measurement in inches, the material and shape greatly influence how a horse accepts a bit of a specific size. These factors affect the required fit.
Mouthpiece Thickness (Gauge)
Horse bit gauges related to diameter are important for comfort.
- Thicker Bits: Distribute pressure over a wider area. They are often better for horses with thick tongues or sensitive bars. They might require a slightly wider overall measurement because the bulk takes up more space.
- Thinner Bits: Concentrate pressure into a smaller area. They are often preferred by light-mouthed or refined horses, but can pinch if the fit is not exact. If you switch to a much thinner bit, you might need to go down a size in width.
Mouthpiece Action (Joints)
- Single Jointed Bits: Apply direct pressure, often causing a “nutcracker” action on the bars and roof of the mouth. They fit best when the width is perfect, as movement can cause pinching if too narrow.
- French Link (Double Jointed): These are generally more comfortable as they relieve direct pressure on the roof of the mouth. They often fit well across a slightly wider range of sizes.
When selecting the right horse bit size, always consider the thickness of the mouthpiece material in relation to your horse’s mouth capacity.
Part 6: Troubleshooting Common Sizing Mistakes
Many riders struggle because they blame the bit size when the issue lies elsewhere. Here is how to check if the fit is the real problem.
Signs a Bit is Too Narrow
- Wrinkling at the Corners: Excess wrinkles or bunching up of the lips on both sides.
- Horse Tries to Put Head Behind Contact: The horse seeks relief by moving its head too low or behind the vertical.
- Constant Chewing/Tongue Play: The horse constantly plays with the bit because it cannot find a comfortable, stationary place for it.
Signs a Bit is Too Wide
- Slippage: The bit slides from side to side in the horse’s mouth.
- Pinching: The corners of the mouth are pulled taut and stretched outwards, potentially causing rubs or sores on the outside lip corners.
- Inconsistent Contact: The rein aids feel muted or vague because there is too much slack in the system.
When to Adjust the Bit Type Instead of the Size
Sometimes, the fit is correct, but the horse rejects the action of the bit. This is where determining correct bit size merges with selecting the right horse bit size based on training level and responsiveness.
- If a correctly sized single-jointed snaffle causes the horse to fight the bit, it might need the tongue relief of a French link, not a different width.
- If a curb bit with perfect width is too strong, the issue is the shank length or curb chain, not the width measurement.
Part 7: Practical Steps for Final Bit Selection
Once you have your measurements, the final selection process involves testing.
The Trial Period
Always try to borrow or use a bit from a tack shop that allows returns or exchanges. Never assume a measurement guarantees success.
- Start in the Middle: If you measure 5.375 inches, try a 5.25 inch and a 5.5 inch bit if available.
- Observe Head Carriage: Ride quietly. Look for relaxed ears, soft eyes, and a steady jaw.
- Check the Corners: After a few minutes of work, pause and look at the corners of the mouth without pulling the reins. There should be slight, even wrinkles.
Record Keeping
Keep detailed notes. If you switch from a 5.25″ D-ring snaffle to a 5.5″ loose-ring snaffle and see improvement, document it. This information is invaluable for future tack choices or when measuring bit cheekpieces on new curb bits.
Summary of Measurement Checkpoints
To ensure you have covered all bases when measuring a horse bit:
- Width: Inside edge to inside edge of the mouthpiece. (Primary measurement)
- Shank/Cheekpiece Length (Curb/Pelham): From the mouthpiece junction to the center of the rein ring. (Determines leverage)
- Chain Fit (Curb/Pelham): Should allow one snug finger in the chin groove when contact is established.
By focusing on these precise checks, you move beyond guesswork and ensure your equipment supports clear, comfortable communication with your horse. This diligent approach to horse bit sizing is key to successful partnership.
Frequently Asked Questions (FAQ)
How often should I check my horse’s bit size?
You should check your horse’s bit size, especially the width, at least once a year, or any time you notice changes in the horse’s mouth (such as weight loss/gain or aging) or if you observe rubbing or pinching when riding. Changes in dental structure due to aging can also affect fit.
Can I use a bit that is slightly too wide for a short time?
Yes, for very short periods (like a quick trail ride), a slightly wide bit is usually less damaging than a slightly narrow bit. However, consistent use of a bit too wide will cause stretching and rubbing at the lip corners.
What if my horse needs a 5.375-inch bit according to the measurement?
Since most bits come in quarter or half-inch increments, you usually choose the closest size. If the horse has thicker lips, go to 5.5 inches. If the horse has thin lips or tends to be sensitive, try 5.25 inches. The horse’s reaction during a short test ride is the final determinant.
Does the cheekpiece length measurement change if I change the mouthpiece type (e.g., from snaffle to curb)?
Yes. When changing from a snaffle (which has no shank) to a curb, you introduce leverage, making the shank length measurement critical. The width measurement, however, is based solely on the horse’s mouth width and remains largely the same unless the new mouthpiece is significantly thicker or thinner.
What are horse bit gauges used for besides width?
Horse bit gauges are primarily used for determining the diameter (thickness) of the mouthpiece and the width. Some specialized sets also measure the length of shanks on curb bits to help standardize the comparison of leverage action, though many riders rely on visual comparison for shanks.