Cost and Quoting

Transformer and Coil Cost Estimation: Building a Quote That Holds

A defensible transformer quote is copper plus core plus labor plus machine time plus scrap recovery plus overhead and margin. Here is how each line behaves and where estimates break.

Material is usually 55 to 70 percent of a transformer's cost, and copper dominates it. At roughly 9.50 dollars per kg for magnet wire including enamel, a unit carrying 0.9 kg of copper across both windings is about 8.55 dollars in conductor before any labor. Core steel adds 2.50 to 4.00 dollars per kg for grain-oriented laminations, so a 2.5 kg core is 8 to 10 dollars. Because copper moves daily, quote the conductor line against a same-week LME reference plus your supplier premium, and state a validity window of 7 to 14 days so a 15 percent metals swing does not eat your margin.

Winding labor is the swing factor buyers underestimate. Machine winding runs 800 to 2500 RPM, but effective output after threading, layer insulation, taps, and tie-off is far lower. Use the Winding Machine Output calculator to convert turns and setup into real minutes: 719 turns at an effective 1200 RPM is 0.6 minutes of spinning, but a full cycle with lead prep and inspection is closer to 6 to 9 minutes. At a loaded rate of 45 dollars per hour, that is 4.50 to 6.75 dollars per winding. The Coil Labor Cost calculator folds setup amortization across the batch so small runs carry their true burden.

Machine time is a separate cost from labor because equipment carries depreciation and maintenance whether or not an operator is dedicated. Charge a machine-hour rate that captures the winder, the impregnation line, and the Hi-Pot Test station. A vacuum pressure impregnation cycle runs 2 to 4 hours per batch but processes many units at once, so the per-unit share depends on batch density. Use the Impregnation Batch Size calculator to spread that cycle cost: a 3 hour cycle costed at 30 dollars per machine-hour is 90 dollars, and across 60 coils that is only 1.50 dollars each, versus 9 dollars each at a 10-unit load.

Scrap and yield quietly move the real cost per good unit. Winding generates copper offcuts, tension breaks, and reject coils, typically 3 to 8 percent of input copper by weight. That scrap is not a total loss because the Scrap Copper Value calculator recovers reclaim value, often 60 to 75 percent of virgin price for clean bright wire, less for enameled or mixed. Model it two ways: gross copper purchased at 9.50 dollars per kg, minus reclaim credit on the 5 percent that becomes scrap at, say, 6 dollars per kg. On 0.9 kg input that credit is about 0.27 dollars, small per unit but material across 10,000 pieces.

First-pass yield at electrical test is the single biggest hidden multiplier. If Hi-Pot and turns-ratio testing reject 4 percent of units, every good transformer must absorb the full material and labor of the failed ones. Divide fully loaded unit cost by the yield fraction: a 30 dollar build at 96 percent yield actually costs 30 / 0.96 = 31.25 dollars per shippable unit. Size your test throughput with the Hi-Pot Test Capacity calculator so testing is not the bottleneck that inflates work in process and hides yield loss until end of month.

Overhead and margin turn cost into price, and this is where quotes get sloppy. Layer factory overhead as a percentage of direct cost, commonly 20 to 35 percent, then add SG&A of 8 to 15 percent, then target margin. A defensible stack for our example: 8.55 copper, 9 core, 6 labor, 3 machine and impregnation, minus 0.27 scrap credit, equals 26.28 dollars direct. Add 28 percent overhead to reach 33.6, add 10 percent SG&A to reach 37, then a 20 percent margin lands the quote near 44 dollars. The Transformer Cost calculator assembles this stack so no line is silently dropped.

Estimates most often go wrong on four inputs. First, using nameplate winding speed instead of effective output overstates capacity and understates labor by two to five times. Second, quoting copper at last quarter's price when the metal moved 12 percent. Third, ignoring setup amortization, so a 50-unit prototype run is priced like a 5000-unit production run and loses money. Fourth, forgetting the yield divisor, which alone is a 3 to 6 percent understatement. Each of these is a single number, and each is worth more than the margin on a typical order.

Sanity-check any quote against a top-down ratio before you send it. For small distribution and control transformers, copper plus core should land near 60 percent of factory cost, labor plus machine near 25 percent, and overhead the rest. If your bottom-up build has labor at 45 percent, you either mispriced the winding cycle or the run is genuinely low volume and should be quoted as such with a setup line item. Rebuild the same unit in the Transformer Cost calculator and the Coil Labor Cost calculator, compare the two totals, and only release the quote when they agree within 5 percent.

Published 2026-07-01.