The measurements you need are the visible screen’s width and height in millimetres, plus your device’s exact model number and whether the glass is flat or curved. Diagonal size, the figure printed on the box or spec sheet, is not enough on its own. Two phones can share the same diagonal measurement and still need completely different protectors.
TL;DR:
- Using width and height measurements in millimetres along with the device model number ensures a proper fit, unlike relying solely on diagonal screen size.
- Curved edges, notches, and sensor placements significantly affect protector compatibility, with corner radius mismatches causing most peeling issues.
- Accurate measurements and model confirmation before purchase, combined with proper installation using alignment tools, prevent sizing errors and reduce returns.
- Large screens require careful measuring of the whole visible panel and checking thickness, as even a few millimetres off can cause fit issues.
- Generic protectors or ones based on screen size alone are unreliable; choosing model-specific protectors based on exact dimensions guarantees better fit and durability.
Table of Contents
- Why diagonal size misleads and what viewable area means
- Measuring your phone or tablet step by step
- Measuring TVs and monitors: extra steps for large screens
- Curved edges, notches and camera cutouts change what fits
- A quick checklist to confirm fit before you buy
- Installation steps that affect whether the size looks right
- How SmartProtectors helps with hard-to-find and borderline sizes
- What actually matters when sizing a protector
- Protectors that match the most common measurement outcomes
- Sources
- FAQ
Why diagonal size misleads and what viewable area means
A diagonal measurement tells you the corner-to-corner distance of the glass, but it says nothing about the shape of that glass, where the bezel sits, or how the corners curve. Two devices can advertise an identical diagonal and still differ in usable width, sensor placement and edge curvature enough to make one protector unusable on the other.
The iPhone 15 tech specs list a width of 71.6 millimetres, while the iPhone 12 specifications list 71.5 millimetres. That’s a difference of just 0.1 millimetres, yet the two phones have different camera cutouts and bezel treatments, so a protector cut for one will not sit correctly on the other despite the nearly identical width.
What this means in practice:
- Diagonal size is a marketing figure, not a fitting measurement.
- Width and height in millimetres describe the actual glass you’re protecting.
- The model number is the fastest way to confirm compatibility without guesswork.
Record the width, height and model identifier together. That trio is the closest thing to a universal, verify-before-buy standard.
Measuring your phone or tablet step by step
You don’t need specialist kit. A millimetre-marked tape measure or a set of digital calipers will do the job, along with a clean cloth and a phone camera to photograph your results.
- Power off the device and wipe the screen clean of dust and fingerprints.
- Measure the width of the visible glass at its widest point, in millimetres.
- Measure the height the same way, top edge to bottom edge.
- Note any camera cutouts, notches or sensor housings and roughly where they sit.
- Check the corners: are they sharply squared or gently rounded?
Write the results down as a short set: width in millimetres, height in millimetres, model number, and a flat or curved flag. Take a photo of the screen next to your tape measure for reference, since it’s easy to forget the exact figures a week later when you’re ready to order.
Pro Tip: If you’re unsure which figures matter, photograph your ruler laid across the screen and send that image to the seller along with your model number. Most sellers can confirm fit from a photo faster than from a description.
Measuring TVs and monitors: extra steps for large screens
Large screens need a longer tape measure and, ideally, a second pair of hands to keep it straight across the full width. Measure the visible panel from edge to edge, then top to bottom, avoiding the outer casing or stand.
- Use a fabric or metal tape long enough to span the whole screen in one pull.
- Record the panel’s depth or thickness when you’re fitting a bezel-mounted or edge-clipped protector, since some designs rely on the frame’s profile.
- Write down the exact model number from the back panel or manual and cross-check it against the manufacturer’s published dimensions before ordering.
A monitor or television with the wrong panel width by even a few millimetres will leave gaps at the edges or fail to clip into a bezel-mounted frame.
Curved edges, notches and camera cutouts change what fits
Curved glass edges are measured by their corner radius, the tightness of the curve where the screen bends toward the frame. A protector cut with the wrong radius will either lift at the corners or leave a visible gap, and that mismatch is one of the most common causes of peeling.
- Photograph the exact position of any notch or hole-punch camera rather than estimating it by eye.
- Note whether the curve wraps fully to the edge or stops at a flat lip, since that changes which protector style will seal properly.
- Favour a case-friendly or slightly smaller protector when your case has a raised lip, and reserve full edge-to-edge glass for cases without one. Our guide to edge-to-edge compatibility covers this check in more detail.
Corner radius mismatches, not width or height errors, cause most of the peeling complaints buyers report after installation.
A quick checklist to confirm fit before you buy
Run through this list before adding anything to your basket:
- Width and height measured and recorded in millimetres.
- Exact model number confirmed against the manufacturer’s own listing.
- Screen type noted as flat or curved.
- Case compatibility checked, particularly around raised lips or curved edges.
- Product listing explicitly names your model, not just your screen size.
If any of those points are uncertain, photograph the screen with your tape measure in shot and send it, along with the model number, to the seller before ordering. Choosing a protector listed for your exact model is consistently the safest route, since generic sizing charts can’t account for every variation in sensor placement or corner curvature.
Installation steps that affect whether the size looks right
A protector that’s genuinely the correct size can still look mismatched if it’s fitted badly. The standard install sequence, as shown in iFixit’s screen protector guide, runs in a fixed order for good reason.
- Clean the screen thoroughly and remove all dust before opening the protector.
- Align the protector using the camera or sensor cut-outs as your reference points.
- Lower it into place without letting it touch down at an angle.
- Squeegee outward from the centre to push out air bubbles.
Alignment trays, included with many packs, hold the protector in the correct position while you lower it, which removes most of the guesswork from step two. Bubbles, trapped dust and cutouts that sit slightly off-centre are frequently mistaken for a sizing error when the protector itself was cut correctly all along. Our bubble-free installation walkthrough and the wet-install method both cover fixes for these snags in more detail.
Pro Tip: If bubbles keep appearing near an edge, lift that section with tape and re-squeegee from the centre out, rather than starting the whole application again.
How SmartProtectors helps with hard-to-find and borderline sizes
When your device isn’t listed, you can submit a request and the seller may source and add it to the catalogue rather than leaving you with a generic, unlabelled fit. Listings across the screen protectors, camera lens protectors and cases note fit details by exact model rather than by diagonal size, and some packs ship with an alignment tray or installation tool built in for exactly the reasons covered above. That combination, exact-model listings plus the right tools in the box, is designed to cut down on the guesswork this guide has walked you through.
What actually matters when sizing a protector
Most sizing advice online still leans on diagonal inches, which is the least useful figure a buyer can act on. The measurement that predicts a good fit is the pair of width and height figures alongside the model number, not the marketing spec on the box.
The other overlooked factor is installation. A correctly sized protector fitted without an alignment tray can look wrong purely from dust or a skewed cutout, and that gets misread as a sizing mistake far more often than it should. If you take one thing from this guide, prioritise recording your model number and millimetre measurements before you shop, and use an alignment tool when you fit the protector. That single habit prevents more returns than any amount of careful shopping around afterwards.
— Dian
Protectors that match the most common measurement outcomes
Once you’ve got your model number and measurements confirmed, matching a protector is straightforward.
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The IMAK Pro+ Full Size Full Glue protector for iPhone 13, 13 Pro and 14 suits readers who confirmed a full-glue, edge-to-edge fit on those models.
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The 3-pack Samsung Galaxy S25/S24 protector with installation tool suits anyone who wants a built-in alignment tray for repeat, precise placement.
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The IMAK Pro+ Series for iPhone 15 is cut specifically for the iPhone 15’s sensor layout rather than shared with older, similarly sized models.
Browse the full screen protectors range to find your exact model, or get in touch if it isn’t listed yet.
Sources
iPhone 15 tech specs, iPhone 12 tech specs, iFixit screen protector replacement guide, and background on display repair and dimensions.
- iPhone 15 - Tech Specs - Apple Support
- How to replace the screen protector on your phone - iFixit Repair Guide
FAQ
How do I know what size screen protector to get?
Measure the visible screen’s width and height in millimetres, then match those figures to your exact device model number rather than relying on the advertised diagonal size. Checking the manufacturer’s own tech-spec page, such as Apple’s iPhone 15 specs, confirms the official dimensions before you buy.
How do I fit a screen protector to my phone?
Clean the screen thoroughly, align the protector using the camera or sensor cutouts as guides, then lower it flat and squeegee outward from the centre to clear any air bubbles. This sequence, detailed in iFixit’s installation guide, reduces the misaligned cutouts and trapped dust that often get mistaken for sizing problems.
Is there a universal cut-to-size screen protector available?
Cut-to-size or “universal” film protectors exist but they can’t account for corner radius, notch position or curved edges the way a model-specific tempered glass protector can. For a reliable fit, choosing a protector listed for your exact device model remains the safer option.
Are iPhone 12 and 15 the same size screen protector?
No. Despite both having similar diagonal screens, the iPhone 15 measures 71.6 millimetres wide against the iPhone 12’s 71.5 millimetres, and the two models differ in camera cutout and bezel design. A protector cut for one will not fit the other correctly.