Film Calculations

How to Calculate Film Throughput, Gauge Variation, Coating Weight, and Drying Energy

Worked examples for the five core film and coating calculations: mass throughput, gauge 2 sigma, dry coating weight, drying energy, and multi pass yield.

Five calculations carry most of the engineering load on a film, membrane, or barrier coating line: extrusion mass throughput, gauge variation, dry coating weight, drying energy, and lamination yield. All five are unit traps. Film thickness arrives in microns, mils, or gauge (100 gauge equals 1 mil equals 25.4 microns), coating weight in grams per square meter or pounds per ream, and line speed in meters per minute or feet per minute. This guide works each formula with real numbers so you can check your own line math before trusting a spreadsheet someone inherited in 2014.

Mass throughput in kg/h equals web width (m) times average thickness (microns) times line speed (m/min) times melt density (g/cm3) times 0.06. A 2.0 m cast line running 50 micron LDPE film (0.92 g/cm3) at 200 m/min moves 2.0 x 50 x 200 x 0.92 x 0.06 = 1,104 kg/h. Work it backward to set line speed: for a 350 kg/h extruder on 25 micron film at 1.6 m width, maximum speed is 350 / (1.6 x 25 x 0.92 x 0.06) = 158 m/min. The Extrusion Throughput calculator handles the unit conversions, including trim width, which you must subtract before quoting salable output.

Gauge variation is reported as 2 sigma percent. Scan 100 or more thickness points across the web with a capacitive or beta gauge, compute the standard deviation, then 2 sigma % = (2 x sigma / mean) x 100. A 25 micron film with sigma of 0.5 micron runs 4.0 percent. The number drives resin giveaway: to guarantee a 23 micron minimum at 4 percent 2 sigma you must average 23 / 0.96 = 24.0 microns, roughly 4 percent extra resin on every kilogram sold. The Film Gauge Variation calculator converts raw scan data into 2 sigma, range, and giveaway so you can set the thickness target instead of padding it by habit.

Dry coating weight in g/m2 (gsm) equals wet applied weight times solids fraction. A gravure station laying down 10 g/m2 of a 30 percent solids adhesive delivers 3.0 gsm dry. Coverage, the number purchasing cares about, is 1,000 / dry gsm = 333 m2 per kg of dry coating. For US converters, 1 lb per 3,000 ft2 ream equals 1.63 g/m2. Verify with a cut and weigh check: a 100 cm2 die cut coated sample minus the uncoated tare, times 100, gives gsm directly. The Coating Weight Yield calculator runs the wet to dry conversion and flags when measured pickup drifts more than 5 percent from the gravure cell theoretical volume.

Drying energy starts with the evaporation load: solvent load in kg/h equals (wet gsm minus dry gsm) times web width (m) times speed (m/min) times 0.06. The 10 gsm wet, 3 gsm dry example at 1.4 m width and 150 m/min evaporates 7 x 1.4 x 150 x 0.06 = 88 kg/h of solvent. Multiply by latent heat, about 366 kJ/kg for ethyl acetate versus 2,260 kJ/kg for water, then divide by oven thermal efficiency, typically 30 to 50 percent, to get burner duty. That water number is why aqueous barrier coatings need far longer ovens at equal speed. The Drying Energy calculator sizes the zones and checks exhaust against LEL limits.

Lamination yield equals good laminate area out divided by primary web area in, tracked per SKU from roll footage counters. A 12,000 m input roll that ships 11,100 m after splices, curl trim, and delamination defects runs 92.5 percent. Multi pass yields multiply: three passes at 96 percent each net 0.96^3 = 88.5 percent, which is why a five layer structure built in two passes beats the identical structure built in three. The Lamination Yield calculator chains multi pass structures automatically. For barrier films, the Barrier Performance Test Load calculator converts OTR and WVTR sampling plans, typically 3 specimens per lot per ASTM F1927 and F1249, into instrument hours so release testing does not become the bottleneck.

Run the calculations in this order when qualifying a new structure: throughput sets the speed window, gauge variation sets the thickness target, coating weight sets the solvent load, drying energy confirms the oven can keep up, and yield tells you how much extra to schedule. Then cross check against a physical roll: weigh a finished roll, subtract the core (typically 0.8 to 2.5 kg for a 3 inch by 1 m core), and back calculate average gauge from logged footage. If the back calculated gauge disagrees with the scanner by more than 2 percent, recalibrate before shipping. Pricing and target setting are handled in the companion cost and benchmark guides.

Published 2026-07-02.