The numbers and letters stamped onto your glasses frame are standardized codes describing the physical dimensions of the eyewear, not your vision correction. These markings are manufacturer-specific but follow a common format, all expressed in millimeters. Understanding these specifications is useful for ensuring a proper fit, especially when replacing an existing pair or purchasing new frames online.
Locating the Frame Specifications
The frame specifications are typically located on the inside surface of the frame components, often in places that are not visible when the glasses are worn. The most common location for the entire string of numbers is the inside of the temple arm, which is the piece extending from the frame front over your ear. If the frame is metal or very thin plastic, the numbers might be split between the two temple arms or the nose bridge.
The inside of the nose bridge is another frequent spot for a portion of the codes, usually the lens width and bridge width measurements. Because the markings are small and often imprinted or laser-etched into the material, you may need a strong light source or slight magnification to read them clearly. Over time, friction and wear can cause the markings to rub off, making it impossible to read the full specifications on older frames.
Decoding the Three Core Measurements
The most important information is presented as a sequence of three numbers, which are standardized measurements for the frame’s size. This sequence is usually separated by a dash, a space, or a small square box symbol (\(\square\)), such as “52 \(\square\) 18 140.” All of these measurements are expressed in millimeters (mm) and are the basis for determining the frame’s fit on the wearer’s face.
The first number is the Eye Size, or horizontal lens diameter, which measures the width of the lens opening at its widest point. This measurement, commonly ranging from 40 mm to 60 mm, is crucial for ensuring the lens is wide enough to accommodate the wearer’s eye and prescription. A larger eye size generally corresponds to a wider frame front overall.
The second number in the sequence is the Bridge Size, which measures the distance between the two lenses where the frame rests on the nose. This measurement typically falls between 14 mm and 24 mm. A correctly sized bridge prevents the glasses from pinching the nose or slipping down the face.
The third and final number is the Temple Length, which is the total length of the arm piece from the frame hinge to the very tip that rests behind the ear. Standard temple lengths often range from 120 mm to 150 mm and are frequently seen in increments of five. Having the correct temple length is necessary for a secure and comfortable fit, ensuring the frames do not press too tightly against the side of the head or hang too far past the ear.
Understanding Additional Frame Markings
Beyond the three core dimensions, other codes and text are often stamped onto the frame, serving primarily as identifiers for the manufacturer and retailer. These additional markings are not related to the frame’s fit but are useful for inventory and replacement purposes. One common marking is the Model or Style Number, which is a unique alphanumeric code assigned by the manufacturer to identify that specific frame design.
The frame may also contain a Color Code or Material Code, which indicates the specific color variation or the material used to construct the frame. This code is helpful when trying to order the exact same frame in a different color or when ensuring a replacement matches the original. The Manufacturer Name or Brand Logo is also typically present, confirming the origin of the eyewear.
Some frames, particularly those sold in certain regions, may also feature safety or regulatory markings. For example, the CE mark indicates that the product complies with health, safety, and environmental protection standards within the European Economic Area. These secondary codes help professionals quickly identify the frame for repair, warranty, or reordering the correct style.
The Difference Between Frame Specs and Vision Prescriptions
The numbers on the frame describe only the physical structure of the glasses and are entirely separate from the wearer’s vision prescription (Rx). The frame specifications dictate the dimensions and fit of the hardware, ensuring the glasses sit properly on your face.
The vision prescription, provided by an eye care professional, contains the specific optical power needed to correct refractive errors like nearsightedness, farsightedness, or astigmatism. This prescription is expressed in diopters and includes values like Sphere (SPH), Cylinder (CYL), Axis, and often the Pupillary Distance (PD). These values dictate the curvature and strength of the lenses that must be cut to fit into the frame.
The frame numbers are useful only for selecting a new frame that is the same size or similar to a pair that already fits well. To order new corrective lenses, the written prescription from an eye doctor is required.