What Is Base Curve—and Why It Matters for Contact Lenses
If you’re new to contact lenses or trying to better understand your prescription and how your lenses fit, the term “base curve” might seem a bit technical. However, this small number plays a big role in determining how well your lenses fit and how comfortable they feel.
What is base curve?
Base curve (often abbreviated as BC) is the measurement of the curvature on the back of your contact lens—the part that touches your eye. It’s expressed in millimeters, usually somewhere between 8.3 and 9.0.
A lower number (like 8.4) = a steeper curve
A higher number (like 8.8 or 9.0) = a flatter curve
The right curve helps your contact lenses stay in place, breathe well, and feel like they’re barely there.
Why does base curve matter?
Everyone’s eyes are shaped a little differently, and your contact lenses should match your unique curves. If the base curve isn’t right for your eye:
Your lenses might feel uncomfortable or shift around
You might experience blurry or fluctuating vision
You could develop irritation or dryness from improper fit
In other words: the right base curve = better comfort, better clarity, and better long-term eye health.
Can I choose my base curve?
Not exactly. Base curve isn’t something you pick out like a size or style—it’s based on the natural shape of your eye and is measured by an optometrist or ophthalmologist.
Your provider will match you with a base curve that fits your cornea well, often during a contact lens fitting appointment. Some lenses come in one standard base curve, but many brands offer multiple options, and your eye care provider will know which is best for you.
Gentle reminder: Even if your prescription numbers look similar across brands, base curve can still vary from one brand to another. Always check with your provider before switching.
Where do I find my base curve?
Look at your contact lens box or prescription—it’ll usually appear like this:
BC: 8.6
DIA: 14.2
DIA stands for diameter, and it works together with base curve to shape the overall fit of your lens.
Can base curve change over time?
Yes—sometimes! Your eye shape can subtly change with things like age, if you’ve had eye surgery, or even during pregnancy! If your lenses suddenly feel different or less comfortable, it’s worth getting a new fitting. Eyes evolve, and your lenses should evolve with them.
FAQ: Base Curve & Contact Lenses
Q: What happens if I wear the wrong base curve?
You might experience blurry vision, discomfort, dryness, or your lenses might shift or fall out more easily. It's best to stop wearing them and check in with your eye care provider.
Q: Can I just guess my base curve if I’ve worn lenses before?
Nope—each brand fits slightly differently. Even if you’ve worn lenses before, a professional fitting is the safest way to find the right curve for your eyes.
Q: Is base curve different for daily vs. monthly contacts?
Not necessarily, but some brands may offer different base curve options depending on the lens type. The key is to stick with what your provider has approved.
Q: Do both of my eyes have the same base curve?
Usually, yes—but not always. Some people have slightly different curvatures in each eye, which would be reflected on your prescription.
Q: How often should I get my base curve checked?
It’s a good idea to have your contacts refitted at least once a year or anytime your lenses feel off.
In Summary:
Base curve = the curve on the back of your lens
It helps ensure your lenses fit comfortably and stay in place
The right base curve supports clear vision and healthy eyes
Always get your base curve measured by an eye care provider
Need help reading your prescription—or finding the right fit?
Chat with us using the help desk at the bottom of the webpage or browse contacts by brand.