Her Perfect Fit Awaits:

A Parent's Guide to Finding the Best Fit

At Once Upon a Charm, we believe finding the right fit should be simple, supportive, and sprinkled with enchantment.

Our girls’ glasses are thoughtfully designed for ages 4 to about 10, with gentle curves and proportions created for little faces.

This Fit Guide will help you understand kids’ glasses sizing, what the measurements mean, and how to choose frames that stay in place, feel comfortable, and look like they were made just for her.


Once Upon a Charm - For the gigglers, the story weavers, the gatherers of treasured trinkets.

A Perfect Fit for Little Faces: Why Kids' Glasses Sizing Matters

Helping her frames stay comfortable, secure and ready for every adventure.

Finding the right fit means more than comfort, it’s about helping her glasses stay in place while she twirls through the garden, builds castles from pillows, or curls up with her favorite storybook. A pair that fits well becomes almost invisible, like a second skin. Light as a breeze and perfectly secure.

That’s why Once Upon a Charm glasses are available in three thoughtfully designed sizes, created to match the gentle proportions of little faces (please note that the age ranges are only guides):

  • Small (44 ☐ 16 - 125) Best for ages 4–5
  • Medium (46 ☐ 16 - 125) Best for ages 5–7
  • Large (48 ☐ 16 - 125) Best for ages 7–11

Understanding Kids' Glasses Measurements: What Does a Size of 46 ☐ 16 - 125 Mean?

  • 46 mm

    This first number is the width of each lens


    Her magical windows, wide enough to see the world with clarity and wonder

  • 16 mm

    The middle number is bridge width

    This is the gentle space that lets her glasses rest softly across her nose

  • 125 mm

    The last number is the length of the temples

    The "temples" are the little arms that tuck behind her ears holding her frames steady through every twirl and tumble
Diagram of frame measurements

And because every story is clearer with a picture, here’s a little sketch to guide you

What is Pupillary Distance and Why is it So Important?

PD, or pupillary distance, is the gentle space between your child’s eyes. It's the place where her vision comes together in perfect harmony.

When her lenses are made, this number helps ensure the center of each of her lenes lines up with the center of each of her eyes. It may sound small, but it’s truly magical. A well-measured PD keeps her vision clear, comfortable, and ready for all the reading, exploring, and adventuring she has ahead.

Some eye doctors will include PD on her prescription. If not, don’t worry. Measuring at home is simple.

At Once Upon a Charm, we know busy parents need options. That’s why we offer three ways to determine your little one’s PD.

Below, you’ll find 3 simple ways to her measure PD. Choose the one that feels easiest for you and your little dreamer.

Illustration of a child in a white coat giving a bunny an eye exam in a forest setting.

Option 1: Call Your Child's Optometrist

If your little one recently had an eye exam, there’s a good chance her pupillary distance (PD) was measured as part of the process, particularly if a prescription was given. You can simply call your optometrist’s office and kindly ask for her PD. 

A gentle note: While many doctors are happy to share this info, some prefer not to (particularly if they hope you’ll purchase glasses directly through their office). Still, it never hurts to ask! After all, this number belongs to your child and is an important part of making sure her vision sparkles wherever she shops for frames. 

Two rabbits in a forest setting using a laptop with 'Once Upon a Charm' on the screen.

Option 2: Use Our Online Measurement Tool

If you'd rather skip the ruler and the guesswork, let our Online PD Measurement Tool do the magic for you! 

How It Works: 

Before you begin, it is important that you sweep your little one’s hair into a ponytail. Pulling her hair up allows our magical tool to see her entire sweet face (ears and all!) for the most accurate fit. 
✦ Choose a frame and start the process to add lenses. Once you get to the Rx section, you will be prompted to measure her PD.
✦ Open the tool on your device (works like a charm on mobile or desktop). 
✦ Follow the simple on-screen instructions. 
✦ Our tool will measure your child’s PD with fairy-precision in just moments. 

Wooden stump in a foggy forest with a ruler on top

Option 3: Measure PD Manually

Prefer a hands-on approach or want to double-check? Measuring PD at home is easier than catching fireflies on a warm summer night, just follow these magical steps!

What You’ll Need:
✦ A ruler with millimeters, preferably transparent (or printable PD ruler)
✦ A hair tie or ribbon
✦ A sprinkle of patience

Follow our step-by-step process below.

Step 1: Pull Her Hair into a Ponytail

Before you begin, tie her hair back to keep the view of her eyes clear and precise. No stray strands means no measurement mistakes!

Step 2: Have Her Sit Still and Look Straight Ahead

Ask your child to sit tall and look at your nose (you may even try putting a sticker on your nose to get her to stay focused).

Step 3: Place the Ruler

✦ Hold the ruler against her brow or gently rest it on her nose.
✦ Align the 0mm mark with one pupil.
✦ Measure to the center the other pupil.

You may want to measure a few times for accuracy or snap a photo to review.

Tip: Most children's PD falls between 43–56 mm. Double-check your measurement for accuracy. Or, take a quick photo to review!

Deer family with pink glasses in a pastel floral background

Fit Tips From Your Fairy Glassmother

When trying on kids’ glasses at home, here’s how you’ll know they fit just right: 

  • The frames sit level. Not too high or too low 
  • Her eyes should be centered in each lens. Use our magical PD measurement tool (see above) to help measure and align her lenses just right. 
  • The temples rest gently behind her ears (no pinching!) 
  • No sliding down = bridge fits well 
  • No red marks = temples and bridge are comfy 

Her glasses should feel like a gentle hug, never a squeeze or a slip.