Bidding low may land you a painting contract, but will you make money? Properly estimating the materials you need for a job is a key skill, and one you have to get right.

Overview

Estimating the amount of paint needed for a roll door repaint project can seem daunting. With hundreds or even thousands of doors to repaint, all with corrugated curtains and different-sized door openings, it is hard to know where to start. However, when broken down, it is not that complicated.

Steps to Estimate Requirements:

1. Determine the actual square footage of each door:

• Door Measurement: Multiply the width by the height of the visible door curtain to get the beginning square footage.
• Corrugation Factor: Most roll door curtains are corrugated, adding an average of about 12% to the total surface area. This needs to be added to the actual door size. Review the actual doors on the job to ensure the corrugation factor is accurate.
• Waste Factor: Spraying extends beyond the edge of the door curtain, requiring an additional waste factor. Typically, an additional 3 inches sprayed around the perimeter of an 8'x8' door equals 6 sq. ft., or about 10% of the door's total footage. Sloppy spraying can increase material usage, so aiming for less than 3 inches of overspray is recommended. A good rule of thumb is to add a minimum of 6 sq. ft. per door as a waste factor.

Formula for Calculating Surface Area:

• (Door width x height) + (12% Corrugation Factor) + (6 sq. ft. Waste Factor) = Actual Surface Area

Example:

• A 7' x 8' door is 56 sq. ft. Adding 12% for the corrugation (approximately 7 sq. ft.), plus another 6 sq. ft. for the waste factor, results in 69 sq. ft. Use this figure of 69 sq. ft. for your material calculations.

Now that you know how to calculate the actual surface area of a door, you can use that to calculate paint material usage.

Calculating Material Usage

To calculate the amount of paint needed for a project, you can divide the surface area by the coverage. For example, if you're painting a 8’x8’ roll-up door with a coating with a coverage of 400 square feet per gallon, you'll need 0.22 gallons of paint (8'x8'/400=0.22 gallons). 

Here are some other things to consider when calculating paint material required: 

• Number of coats

The number of coats required will affect how much paint is needed. Products like Chem-Bake One-Step generally cover with one coat, even over color changes.

Note: Depending on the paint product you choose and how extreme the color change is, additional coatings may be required. In these cases or you decide that the underlying paint requires primer, a bonding primer tinted to a similar shade as the new color can be much less expensive than using two coats of a more expensive performance paint.

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