Last summer, I made a $250 mistake.
Bought new prescription glasses. Loved them. Then walked outside and got blinded by the sun. So I ordered fitovers online. They showed up three days later and didn’t fit. Too tight. Pressed against my frames. Looked awful.
Returned them. Tried again. Same problem.
The third time, I finally got smart and actually measured my glasses first. Worked perfectly.
That’s what I’m sharing today. The simple measurement process that works every time. Takes two minutes. Saves you from returns, refunds, and frustration.
Why Measuring Actually Matters
I know measuring sounds boring. You just want to buy sunglasses.
But here’s what happens when you skip it – you’re guessing. Maybe they’ll fit. Maybe they won’t. You order them, wait for shipping, they arrive, and… nope. Too small or too big. Now you’re dealing with returns.
Been there. It sucks.
When you measure first, your fitovers fit the first time. Comfortable. Look good. Actually enjoyable to wear instead of giving you headaches or letting light leak in everywhere.
The process isn’t hard. Ruler and two minutes. That’s it.
What You Need
Don’t overthink this. Here’s what I use:
A ruler – Needs millimeters on it. Most fitover brands use millimeters, not inches. A regular 12-inch ruler works great.
Your prescription glasses – The ones you’ll wear under the fitovers. Not that old backup pair you never use.
Something to write with – Phone notes app works fine. You need these numbers when shopping.
That’s everything.
Some people buy digital calipers. Sure, they’re precise. But honestly? A regular ruler works just as well. I’ve used both and can’t tell the difference.
The Two Measurements That Matter
Fitover sizing is simple. Width and height. That’s it.
Get these right and you’re done.
Measuring Width
The width goes across your glasses horizontally.
Take off your glasses. Put them on a table facing you. Find the widest spots on the outer edges – usually near the temples or corners.
Put your ruler across those points. Measure the left edge to the right edge. The whole frame – both lenses plus the middle bridge.
Write it down in millimeters.
Most prescription frames are 125mm to 145mm wide. If yours is way different (like 100mm or 170mm), check again. You probably measured wrong.
Measuring Height
Height is top to bottom on your frames.
Keep your glasses on that flat surface. Find the highest point at the top. The lowest point is at the bottom. Measure straight down between them.
Important bit: measure the full frame opening, not just the lens. Include the frame edges.
Write that number down too.
Most frames are 35mm to 50mm tall. Way outside that range? Measure again.
Quick tip: Keep your ruler straight. I’ve seen people measure at an angle and get totally wrong numbers.
Converting Inches to Millimeters
Maybe your ruler only has inches. No problem.
Multiply inches by 25.4 to get millimeters.
Example: 5.5 inches × 25.4 = 139.7mm. Round up to 140mm.
Common conversions:
- 5 inches = 127mm
- 5.25 inches = 133mm
- 5.5 inches = 140mm
- 5.75 inches = 146mm
- 6 inches = 152mm
Always round up when between numbers. Bigger is better than smaller for fitovers.
Understanding Size Labels
You’ve got measurements. Now what?
Brands use different sizing systems. Small/Medium/Large. Actual measurements. Style names with size ranges. Kind of annoying.
General breakdown:
Small:
- Width: 125-135mm
- Height: 35-40mm
Medium:
- Width: 135-145mm
- Height: 38-44mm
Large:
- Width: 145-155mm
- Height: 42-50mm
But here’s the thing – don’t just trust labels. Different brands define “medium” differently. Always check their specific size chart.
The Rule You Can’t Break
Fitovers must be bigger than your prescription frames. Not the same size. Bigger.
Why? They wrap around your existing glasses. Same size or smaller means they squeeze your frames. Creates pressure. Makes everything uncomfortable. Sometimes, it scratches your lenses.
What works: Add 5-8mm to each measurement.
Your frames are 138mm wide and 40mm tall? You need fitovers that fit at least 143mm by 45mm.
Most brands call this “internal measurement” or “maximum frame size.” That’s the biggest prescription frame that fits inside.
Always compare your frame measurement to their internal measurement. Apples to apples.
Step-by-Step Process
Here’s exactly what I do:
Step 1: Clean your glasses. Put them on a flat surface.
Step 2: Position them facing you (front view).
Step 3: Get your ruler. Find the widest points on the outer edges.
Step 4: Measure straight across. Record width in millimeters.
Step 5: Find the highest point at the top, the lowest at the bottom.
Step 6: Measure straight down. Record height in millimeters.
Step 7: Add 5-8mm to both numbers. Those are your minimum fitover sizes.
Step 8: Check the brand’s size chart. Find fitovers that accommodate your adjusted measurements.
Done. Ready to order.
Takes maybe three minutes if you’re careful.
Matching Shape to Your Frames
Measurements are crucial. But style matters too.
Your frames have a shape. Rectangular, round, cat-eye, whatever. Your fitovers should work with that shape.
Rectangular frames?
Get rectangular or wraparound fitovers. Same lines. Looks cohesive.
Round frames?
Round or oval fitovers work best. Echo that circular shape.
Cat-eye or angular frames?
Choose fitovers with similar angles. Curved styles will clash.
Aviator or big frames?
Need larger fitover styles. Small fitovers over big frames look ridiculous.
Some companies design specific models for specific shapes. Check their recommendations.
Finding Quality Fitovers That Last
I’ve tried tons of fitover brands. Cheap gas station ones. Mid-range optical shop ones. Premium online ones.
Myliia stands out.
Their polarized lenses actually eliminate glare. I’ve bought “polarized” fitovers that were just dark lenses. Myliia’s work is proper. You notice immediately when driving.
They use multi-layer coatings. UV400 blocks harmful rays. Anti-reflective cuts eye strain. Scratch-resistant keeps them clear for years.
For fit, they design frames with proper internal clearance. Cheap fitovers squeeze your prescription frames. It gives you room.
Materials matter too. Cheap fitovers crack within weeks. The fitovers from Myliia are built to last – I’ve been using mine for over a year without issues. You pay more upfront, yeah. But they’ll work great two years from now instead of breaking after a month.
Follow my measurement guidelines, and Myliia fitovers will fit your prescription glasses properly. Made for people who want protection and comfort without looking goofy.
Common Mistakes to Avoid
Mistake #1: Only measuring width
You need both dimensions. Height matters just as much.
Mistake #2: Measuring your face instead of frames
Fitovers go over glasses, not on your face. Measure the frames.
Mistake #3: Ordering the same size as the frames
Fitovers need to be bigger. Add those extra millimeters.
Mistake #4: Using bent or old frames
Measure the glasses you actually wear. Bent frames give wrong measurements.
Mistake #5: Forgetting frame shape
Wide, shallow frames need different fitovers than narrow, tall ones.
Mistake #6: Ignoring the brand’s specific chart
Every manufacturer is different. Check their actual measurements.
I’ve made most of these myself. Learn from my failures.
Between Sizes? Go Bigger
Sometimes measurements fall between two sizes.
Happened to me last month. Frames were 142mm wide. One style maxed at 142mm. The next size started at 145mm.
Which to pick? Go bigger. Always.
Slightly too big still works. Might feel loose but they’ll block light and protect your eyes.
Slightly too small doesn’t work at all. They squeeze, sit crooked, make everything uncomfortable. Can’t fix that except by returning them.
Really unsure? Contact customer service. They’ve answered this question a thousand times.
Testing Fit When They Arrive
The package shows up. How do you know they fit right?
Quick test:
Put prescription glasses on first. Slide fitovers over them.
Check sides: Should see a few millimeters of clearance on each side. No touching or rubbing.
Look at the top and bottom: Same clearance there.
Test bridge: Fitovers rest on the nose without pushing prescription glasses down.
Check light gaps: Small gaps are okay. No big openings where light streams in.
Move around: Turn your head side to side. Look up and down. Bend over. Should stay secure.
Everything good? Perfect.
Something off? Don’t settle. Contact them about exchanges.
Track Your Measurements
Your prescription changes. Frames change. Fitover needs to change.
I keep a note in my phone: “Glasses Measurements.” Update it with new frames.
Before buying fitovers, check that note. Verify sizes match. Order confidently.
Takes 30 seconds. Saves ordering the wrong sizes months later.
Take fresh measurements if:
- You get new prescription glasses
- Frames get bent or adjusted
- You want fitovers for different glasses
- Been over a year since the last measurement
Frames shift over time. Quick remeasure keeps things accurate.
What to Remember
Main points:
Measure both the width and height of prescription frames. Use millimeters. Add 5-8mm when shopping for fitovers.
Match styles to frame shape. Check each brand’s specific chart. Between sizes? Go larger.
Don’t rush. Two minutes measuring beats two weeks of returns.
Quality matters. Premium fitovers like Myliia offer better materials, real polarization, and proper clearance.
Take Action Now
You know how to measure fit-over sunglasses.
Do this right now:
Grab your prescription glasses and ruler. Measure width and height. Write numbers down.
Add 5-8mm to each. Those are your target sizes.
Look at brands making quality fitovers in your range. Compare their charts to your measurements.
Order confidently. You did the work. Got accurate numbers. Fitovers will fit perfectly.
No more squinting. No more expensive prescription sunglasses. Just comfortable fitovers that work with the glasses you own.
