Core Formulas

How to Calculate Roll Forming Yield, Throughput, and Coating Coverage for Roofing and Siding

The core formulas that turn a coil weight and a line speed into finished squares of roofing and siding, worked through with real units.

Start with coil yield, because every downstream number depends on it. Linear feet from a coil equals coil weight in pounds divided by the weight per linear foot, where weight per foot equals coil width in feet times gauge thickness in feet times 40.8 for steel (steel density is 490 lb per cubic foot). A 12,000 lb coil, 43.25 inches wide (3.604 ft) at 26 gauge (0.0187 in, or 0.001558 ft), weighs 3.604 x 0.001558 x 490 equals 2.752 lb per foot. That coil runs 12,000 / 2.752 equals 4,361 linear feet. The Coil Yield by Profile calculator handles the profile-specific coverage width automatically.

Convert linear feet to squares (100 sq ft of coverage) using the exposed coverage width, not the coil width. A 43.25 inch coil formed into a panel with 36 inches of net coverage yields 3.0 sq ft per linear foot. So 4,361 ft times 3.0 equals 13,083 sq ft, or 130.8 squares from that one coil. The difference between the 43.25 in entry width and 36 in coverage is your forming take-up plus trim, roughly 17 percent of the strip consumed by ribs, seams, and edge trim. Track that ratio; it is the single biggest driver of material per square.

Throughput is line speed times uptime times yield. If the roll former runs 120 feet per minute (fpm) and you form 36 in coverage panels, raw rate is 120 x 3.0 equals 360 sq ft per minute, or 3.6 squares per minute. Over a 480 minute shift at 78 percent availability you get 480 x 0.78 x 3.6 equals 1,348 squares. Feed the fpm, coverage width, and availability into the Roll Forming Throughput and Line Speed Capacity calculators to compare a 120 fpm line against a 180 fpm line before you commit to a delivery date.

Scrap trim cost per square starts from the trim fraction. If entry width is 43.25 in and coverage is 36 in, trimmed and take-up material is (43.25 - 36) / 43.25 equals 16.8 percent of the strip. On steel at 0.95 dollars per pound and 2.752 lb per foot, each linear foot carries 2.61 dollars of metal; 16.8 percent of that, 0.44 dollars per foot, is non-coverage material. Divided across 3.0 sq ft per foot, that is 0.146 dollars per sq ft, or 14.60 dollars per square lost to trim before any prime scrap. The Scrap Trim Cost calculator isolates recoverable versus dead loss.

Coating coverage is a dry-film math problem. Coverage in sq ft per gallon equals 1,604 times percent solids by volume divided by dry film thickness in mils. A 55 percent solids coating applied at 0.8 mils dry gives 1,604 x 0.55 / 0.8 equals 1,103 sq ft per gallon. For a two-coat system (0.2 mil primer plus 0.8 mil topcoat) you run each pass separately and add the gallons. Enter solids, target mils, and both sides of the sheet into the Coating Cost per Square calculator; a coil coater covers both faces, so double the demand for a painted-both-sides SKU.

Color changeover loss is measured in feet of purge, not minutes. If a color change purges 90 linear feet of coated strip and you run 14 changeovers per shift, that is 1,260 feet scrapped. At 3.0 sq ft per foot and a 26 dollar per square landed value, changeover scrap alone is 1,260 x 3.0 x 0.26 equals 983 dollars per shift. The Color Changeover Loss calculator lets you test whether sequencing light to dark cuts your average purge from 90 feet to 60 feet, which on 14 changes recovers roughly 328 dollars a shift.

Installer kit and packaging math close the loop. Panels per bundle equals target bundle weight divided by panel weight; a 12 ft panel at 2.752 lb per foot weighs 33.0 lb, so a 75 lb handling limit caps you at 2 panels plus fasteners, or you drop to a 10 ft cut. Fasteners follow coverage: at 80 screws per square for exposed-fastener panel, a 130.8 square coil needs 10,464 screws. The Installer Kit Quantity and Packaging Length Optimization calculators size the fastener count, closure strips, and pack length so a job ships complete.

Sanity check every result against a mass balance. Coil pounds in must equal coverage pounds plus trim pounds plus prime scrap; if the three do not sum to the coil weight within 1 to 2 percent, an input is wrong, usually gauge or coverage width. Re-run the Coil Yield by Profile figure, confirm gauge with a micrometer (26 gauge steel is 0.0187 in, not 0.019 in nominal), and verify coverage on the formed part with a tape. Getting these four numbers, yield, throughput, trim, and coating, correct is the foundation for any quote or KPI you build later.

Published 2026-07-01.