If there’s a fourth number listed, then it represents the lens height at its tallest point.

You can use a glasses ruler that’s specifically used to measure your eyes for a more accurate home measurement. If you want to measure an old pair of glasses, find the width between the lenses at their narrowest point. Bridge sizes that are too narrow could pinch the sides of your nose, but too wide of a bridge could make your glasses slide off your face.

If your frames are too wide, then it could make your face look imbalanced. If your frames are too narrow, your glasses may feel too tight and get uncomfortable pretty quickly. To get a rough estimate of the lens width for your glasses, subtract your bridge size from the frame width. Then, divide that number by 2. For example, if your frame width is 125 mm and your bridge size is 18 mm, then 125mm−18mm=107mm{\displaystyle 125mm-18mm=107mm}. Then, 107mm/2=53. 5mm{\displaystyle 107mm/2=53. 5mm} for the lens width.

To measure the temple arms on an old pair of glasses, find the distance from the hinge to the tip of the arm. There’s not really an easy way to measure your face to determine the temple arm length. Try a few pairs of glasses on and check their sizes to see what feels best for you.

Ask a friend to help you to take a more accurate measurement. Try using an app like GlassesOn or EyeMeasure to help you measure your PD based on a photo. Some online glasses retailers like Warby Parker have online tools to take measurements for you. If you don’t want to measure your pupillary distance yourself, check if the measurement is listed on an old prescription you have. If you can’t find it, then make an appointment with your optometrist.

If your glasses leave red marks on your nose, then it’s a sign that your frames are too tight. Adjust the nose pads if you can so they have a looser fit. If your glasses don’t have nose pads, stick on adhesive pads under the bridge to help them fit better.

For bifocals, the line on the lens should line up with the highest point on your bottom eyelid. [9] X Research source

If your eyebrows are close to your eyes, then also avoid half-frame glasses since they make your face feel a little imbalanced.

If your glasses feel loose or slide off your face, then the arms are too long or the frames are too big for you. You can try using a glasses strap to hold your glasses tighter.

If you have an oval face, try square or rectangular frames. For a round face, try oversized rectangular or square frames. For a square-shaped face, try rounded or cat-eye frames. If you have a narrow face, then try to get glasses that are a little wider to help balance out your face.