How to Find Your Sunglasses Size
You can find your sunglasses size by measuring your face for the best fit. Take a ruler and measure the distance between your left and right temples and the distance from your hairline to the bottom of your chin. Then, measure the width of your forehead from one side of your hairline to the other. Take your measurements and put them together to determine the shape of your face so you can choose sunglasses that suit you. If your face is square-shaped, choose glasses with rounded bottom edges. Try rectangular glasses if you have a rounder face and choose glasses that are larger at the bottom if you have a long face or narrow chin to complement your shape.
Use a ruler to measure from cheekbone to cheekbone. Using a measuring tape or ruler, measure the distance between your left and right temples. Place the tape measure at the very top of your cheekbone, just below eye level, and stretch it to the same point on the other side of your face. Make a note of the number. Measure your jawline. Place the end of the tape measure just below your ears and find where your jawbone begins. Measure from one end of your jawbone to the other around the bottom of your face. Write this down too. This is an important measurement in determining the shape of your face. Take note of your face length. Measure from the beginning of your hairline down over your nose to the bottom of your chin. Write this measurement down as well. This will help you determine which lens height is best for your face. Write down your forehead width. Measure the width of your forehead from one side of your hairline to the other. Write down this number with the rest of your measurements. This number, along with your cheekbone measurement, will give you an idea of which frame width you should choose. Use these measurements to determine the shape of your face. This is an important step in deciding which frames are best for you. While the fit is ultimately most important, you also want to make sure the style compliments your face. Ideally, you want your glasses to balance the natural proportions of your face. While faces come in all shapes and sizes, most can be lumped into either square, triangle, oblong, round, or oval. Oval faces are complemented by any shape and style of frame shape. Use your current frame size for reference. The frame size is typically found on the inside of the temple arm or nose bridge, depending on the manufacturer. The eye/lens size is usually first, followed by the bridge size, then temple size. The eye/lens size is generally used to determine the best frame size. You have a margin of 3 millimetres (0.12 in) on each measurement, except for the bridge. Stick to a margin of just 2 millimetres (0.079 in) on the bridge. Frame width will not be printed on the frame. Follow the guide below in order to accurately measure frame width and ensure the perfect fit. Take your own measurements of old glasses. Don't worry if the numbers aren't printed on your glasses. You can always use a ruler or measuring tape. To start, measure the frame width horizontally across the entire front of the frame. Make sure to include any bolt or hinge that sticks out on the side! Then, measure the temple arms from the hinge to where they begin to bend around the ear. After that, measure from the top of the bend to the bottom tip. Add the two measurements together for the total temple length. The lens height is measured vertically at the tallest point of one lens. The bridge is measured horizontally, at the top of the bridge, from the edge of one lens to the other. Use a credit card to measure your face. If you are in a pinch and can't find a ruler or tape measure, you can use a credit card. While lens size may vary by brand, most credit cards are the approximate width of a standard size lens. Using a mirror, take a credit card with one hand and hold the edge against the bridge of your nose and under your eyebrow. Note where the other edge ends. If the end of the card aligns with the end of your eye, you should be comfortable with a standard size. If the card extends beyond the end of your eye, you should consider a smaller size. On the other hand, if the card does not reach the end of your eye, you should opt for a larger size. Wear sunglasses that have rounded bottom edges if your face is square shaped. As a rule, you should avoid any glasses with boxy or angular corners. Those with square faces are complemented well by wayfarer glasses. This style will help give your face a rounder silhouette. Choose sunglasses that are heavier at the bottom if you have a long face or narrow chin. This will help shorten oblong faces. In general, you should stick to glasses with wider lenses. Longer faces are complimented well by aviators or more modern sport sunglasses. Try rectangular glasses if you have a rounder face. More angular frames will balance the roundness of your face. This could be the perfect opportunity to try a more retro or vintage pair of glasses. Make sure your glasses fit just right, as smaller glasses can make your face appear overly heavy. Make sure the frame material suits your purposes. There are many different options to choose from, depending on your needs. Plastic or metal are the most common frame materials. There is also nylon or titanium if you need a more lightweight or hypoallergenic option. Nylon is typically used for sport and performance frames. While plastic is often the cheapest option, plastic frames will break easier than metal or steel. Choose the lens material wisely. As with frame material, there are a variety of lens to choose from. Typically plastic or Polycarbonate lens are the cheapest. However, a higher index plastic lens will be thinner and lighter than a polycarbonate one. Polycarbonate is the softest lens material and also the most impact resistant. You want to make sure that your lenses will protect your eyes from harmful UV radiation. The good news is that polycarbonate and nearly all high index lenses have 100% UV protection built in. 
Use a ruler to measure from cheekbone to cheekbone. Measure your jawline. Take note of your face length. Write down your forehead width. Use these measurements to determine the shape of your face. Use your current frame size for reference. Take your own measurements of old glasses. Use a credit card to measure your face. Wear sunglasses that have rounded bottom edges if your face is square shaped. Choose sunglasses that are heavier at the bottom if you have a long face or narrow chin. Try rectangular glasses if you have a rounder face. Make sure the frame material suits your purposes. Choose the lens material wisely. 