What Does 20×50 Mean For Binoculars?

You can feel overwhelmed when shopping for binoculars, especially with the avalanche of data that manufacturers and reviewers provide. Determining what the various numbers mean is critical, however, if you want to make a well-informed purchase. For example, what does 20×50 mean for binoculars? Let’s take a closer look at the number x number formula and discuss what it can reveal about the optics it describes.

A Common Formula

As you shop in-store or online for binoculars, you will notice that each pair has a spec listed in this formula: first number x second number. The first number in this equation indicates the magnification power that the optics provide. A second number follows the x and it indicates the objective lens diameter for the binoculars in question. These numbers, taken individually or together, can tell you a lot about the viewing quality of that product.


The listed magnification power (the first number in the formula) indicates how many times larger an image appears through the ocular lenses than it does with an unaided eye. In the case of the formula 20×50, the 20 indicates the magnification power. A pair of binoculars with this magnification would produce an image that is 20-times larger than what you would see with your eyes alone.

Keep in mind that the more an image is magnified, the harder it will be to keep that image steady. Many users find a magnification of 8 or 10 to be the highest that they can keep steady with their hands before a tripod or another type of platform is needed. A pair of binoculars with 20 times magnification would likely be difficult to keep steady and would benefit from a tripod.

Objective Lens Diameter

A binocular’s objective lens diameter (the second number in the formula) shows the width of the front lenses that are closest to the object being viewed. These lenses are used to gather light photons. The wider the lens, the more light that can be gathered. This number is listed in millimeters (mm).

Our eyes use light photons to see. As an objective lens gathers light, it helps to provide a clearer image that is sharper in detail. Of course, larger lenses will also mean more bulk and weight are added to the binoculars. A pair of binoculars with 50mm object lenses will gather a decent amount of light photons but will be larger and heavier.

Seeing It All Together

A pair of 20×50 binoculars will magnify 20 times and employ objective lenses of 50mm diameter. These binoculars will provide an exit pupil of 2.5mm (objective lens divided by magnification). This provides plenty of daylight power with decent cloudy or late-afternoon visibility. You might want to add a tripod for stability, however.

A good place to compare products and features can be found here. Remember to keep the number x number formula in mind as you research and try to match it to your viewing needs!