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How Do Paper Stocks Get Their Grades?

May 14, 2017

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While most of us are aware that paper comes in different stocks, we’re not always sure which stock to use for any particular application.

Generally, there are two ‘grades’ or numbers that are assigned to each type of office paper that will help you choose the best one for your purposes. One grade is the weight of the paper and the other grade is the paper brightness or whiteness.

The Weight Grade

Expressed in pounds, a paper’s weight grade is determined by the actual weight of 500 17” x 22” sheets of the particular paper. So 500 17” x 22” sheets of regular 20 lb. copy paper weighs 20 pounds. The heavier the paper, he thicker each sheet will be.

The Brightness/Whiteness Grade

This grade is a measure of the reflectivity of the paper. The higher the number, the more reflective, and ‘brighter’ or ‘whiter’ the paper. Technically, a brightness/whiteness grade of 100 would mean the paper reflects all the light that hits it, but, as you’ll see below, brightness and whiteness can go off the scale.

There’s a bit of confusion about the differences between ‘brightness’ and ‘whiteness’, but most common available papers usually feature a brightness number (even while their packages proclaim ‘bright white’).

Just so you know, brightness is a measure of the paper’s reflectance of blue light. Whiteness measures the paper’s reflectance of white light, which is the full light spectrum, so it relates more to how our eyes see the actual ‘brightness’ of the paper.

Brightness and whiteness grades can sometimes exceed 100 when Optical Brightening Agents (OBAs) are added to the paper. OBAs reflect UV light as visible light, which increases the brightness of the paper because it reflects more visible light than what’s in the source light.

Some OBAs are fluorescent, which makes them ‘whiter’ and puts their whiteness grade over 100.

So now you know where the numbers on the paper packages come from, you can start to make better choices for which paper grade to choose for different printing applications.

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