How To Determine Paint or Coating Coverage Spread Rates
by William Rice

If you want to find out how far any paint or coating will cover, you should be thankful to a paint instruments developer named George Pfund. He gave us the Pfund Formula for Determining Paint Spreading Rates.

Understand, this formula does NOT speak to a paint or coatings quality or applicability to perform at a given level of protection. It speaks ONLY to how far a gallon of paint or coating will cover. For it to be useful, you have to know two things: the solids percentage in a paint, AND the thickness of dry film you desire.

The formula states at a thickness of one mil, with a coating containing of 100% solids, the coverage rate will be approximately 1630 square feet per gallon. For example, if you know that your coating has 50% solids, at a thickness of one mil, the coating will have a spread rate of 815 square feet. Further, the same coating applied 2 mils thick would have a coverage spread rate of 407.5 square feet.

So, reducing the thickness you want to apply a coating at increases the coverage spread rate. Just as increasing the thickness you apply it at will reduce the coverage rate in equal proportion to the increase or decrease in thickness of the applied coating, GIVEN that the coating being calculated upon stays of the same solids percentage content.

The same thing can be said about solids content. Reducing the solids content that a coating has will decrease the spread coverage rate, just as increasing solids will increase the coverage rate, given the same application thickness.

We include the Pfund Formula as a general resource to anyone considering any painting project with any product, ours or others. It gives you a quick calculation of what your coverage should be in a best-case world. But, the real world can be a somewhat different place.

In the real world, surfaces can be rough, not completely smooth. This, like the other real world conditions we will get to in our discussion, can reduce the coverage you get by a little or a lot. How so? A rough surface will take more coating to cover it because the roughness of the surface acts like tiny hills and valleys into which the coating must go. The rougher it is, the less coverage you will get.

If you are spray painting outside, you may have wind to contend with. Spraying with any type equipment will be less efficient when wind blows against what is being sprayed; it makes for a less than ideal spray pattern. The windier the day is, the less coverage you will get. Ideally, you would spray when there was no wind, but sometimes there are exigencies that cannot be helped.

Once again, if you are spraying your project, in the real world, your equipment and your technique will effect coverage rate. As noted in the Spraying Guide, guns have different transfer efficiencies and sprayer's technique, particularly in overlapping, can have a dramatic effect on coverage rate.

We tell you this so you will know what the truth really is and have realistic expectations when using any manufacturers paint or coating. And, also because many of our competitors offering "me too" products, use thickness of material and expected coverage rates to confuse and deceive you into believing they can give you something for nothing. We suppose that is their right, but; it is also your right to know the reality behind what is offered to you. It's your money; do as you think best. But, remember the old adage popularized by Nobel prize winning economist Milton Friedman, TANSTAAFL...THERE A'INT NO SUCH THING AS A FREE LUNCH.