Nominal Size vs. Actual Size

Whether you are measuring lumber or air filters, it is important to note that the nominal size is not the same as the actual size. But what does nominal size mean anyway? Learn the difference between the two dimensions and make your air filter purchase with confidence.

What is Nominal Size?

Nominal dimensions refer to the rounded number used on the label packaging of both air filters and lumber.

Nominal Size vs. Actual Size: How are They Different?

Once you understand that nominal size is not an exact measurement, but rather a rounded number that makes searching for a filter and packaging lumber more efficient, you can infer how that differs from the actual size. The actual size refers to the exact measurements of your air filter, and the true dimensions when you measure the length, width, and depth (thickness). Actual size typically includes a fraction number within the dimensions – for example: 19 1/2" x 19 1/2" x 3/4". Since air filters are most often sold by their nominal dimensions, it is crucial to learn how to properly measure your air filter. When making your purchase, you should order your filter by its nominal size, rather than its actual size.