Replacing a watch glass is a common repair that can breathe new life into an old or damaged timepiece. However, ensuring the replacement glass fits perfectly requires accurate measurements. This guide will walk you through how to measure for watch glass and provide helpful tips to guarantee a precise fit.
Types of Watch Glass
Before measuring, it’s essential to understand the different types of watch glass available:
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Mineral Glass – Durable and scratch-resistant, often used in mid-range watches.
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Sapphire Glass – Highly scratch-resistant and found in high-end watches.
- Acrylic Glass (Plexiglass) – Lightweight and affordable, but prone to scratches.
Each type requires accurate measurement to ensure a snug fit within the watch bezel.
Tools You’ll Need
- Digital Calliper (highly recommended for precise measurements)
- Micrometre (optional but useful for accurate thickness measurement)
- Cleaning Cloth (to keep the watch case and measuring tools clean)
Step-by-Step Guide to Measuring for Watch Glass
Step 1: Remove the Old Glass
If the original glass is intact, remove it carefully so you can take the measurements. If it’s broken or missing, you’ll need to measure the inner diameter of the bezel instead.
Tip: Use a watch case opener if the glass is press-fitted or secured with a bezel ring. For watches with screw-down bezels, unscrew the bezel first.
Step 2: Measure the Diameter
Using a digital caliper, measure the inner diameter of the watch bezel in millimetres (mm). This measurement will determine the size of the replacement glass.
Measure twice to ensure accuracy.
Be sure the calliper is positioned squarely across the centre of the bezel for the most accurate reading.
Note: Replacement glass sizes are usually given in millimetres (e.g., 30.5mm, 32.0mm). Always round to the nearest 0.1mm for the best fit.
Step 3: Measure the Thickness
If the thickness of the glass matters for your watch case (common for waterproof models), use a micrometre to measure the thickness of the original glass or the space available in the bezel.
Common thicknesses:
- 1.0mm to 1.5mm for standard watches
- 2.0mm to 3.0mm for high-pressure or dive watches
Step 4: Determine the Glass Shape
Watch glass can come in several shapes, such as:
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Flat – Most common and used in many modern watches
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Domed – Offers a vintage look and additional strength (sometimes called 'Single Domed')
- Double-Domed – Reduces distortion and glare, ideal for high-end watches
Choose a replacement glass shape that matches the original to maintain the watch’s appearance and functionality.
Tips for Ensuring a Perfect Fit
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Use High-Quality Measuring Tools: Cheap callipers may lead to inaccurate measurements. Invest in a reliable digital calliper.
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Check for Bezel Irregularities: If the bezel is bent or damaged, the measurements may not be accurate. Repair or replace the bezel if needed.
- Order the Correct Shape and Thickness: Incorrect thickness or shape may prevent the glass from sitting flush in the bezel, compromising the watch’s water resistance.
Replacing the Watch Glass
Once you have the correct size, install the replacement glass carefully:
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Clean the Bezel: Remove any dust, debris, or old adhesive from the bezel.
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Position the New Glass: Align it carefully over the opening.
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Press the Glass Into Place: Use a watch crystal press for even pressure and a secure fit. Some watches may require a clear drying glue to hold the glass in place.
- Test for Fit and Water Resistance: Ensure the glass sits flush and test for water resistance if applicable.
Measuring for watch glass requires precision and attention to detail, but with the right tools and techniques, you can ensure a perfect fit. Whether you’re replacing glass on a vintage timepiece or a modern dive watch, following these steps will help you achieve professional results.
Explore our full selection of watch glass and repair tools and get started on your next watch repair today!