Cost & Quoting

Rotational Molding Cost Estimation: How to Quote a Rotomolded Part

A money-first breakdown of what drives rotomolded part cost, how to build the quote line by line, and the estimating errors that quietly kill margin.

Resin is usually the single largest line in a rotomolded quote, often 40 to 60 percent of total part cost. Price it on delivered shot weight, not nominal wall, because grinding and purge losses are real money. If LLDPE runs 1.65 USD per kg and a part takes a 7.0 kg charge, that is 11.55 USD before color. Add 3 percent pigment at 4.50 USD per kg (0.21 kg = 0.95 USD) and you are near 12.50 USD in material alone. The Resin Cost Per Part calculator pins this down; a 0.10 USD per kg resin move shifts a 7 kg part by 0.70 USD, which matters across a 5,000-part contract.

Machine time is the second driver and the one estimators most often underprice. Cost it as a fully burdened machine-hour rate, typically 60 to 120 USD per hour for a mid-size carousel depending on gas cost and depreciation. A 54-minute total cycle on a single arm at 85 USD per hour is 76.50 USD of machine time. If that arm can carry two molds, the per-part machine cost halves. Mold Arm Utilization and Mold Capacity Per Shift tell you how many parts truly come off per shift, and that throughput number, not the cycle alone, sets the real machine cost per unit.

Labor should be quoted per mold serviced, not per shift averaged, or you will hide the cost of complex parts. A manual load, spray, insert placement, and demold cycle can run 6 to 12 minutes of direct labor per part at a loaded rate of 28 to 40 USD per hour, so 8 minutes at 34 USD is about 4.50 USD. Parts with foam-in-place, threaded inserts, or graphics take two to three times that. Track it against the servicing time you already used in cycle planning so the labor in your quote and the labor in your schedule are the same number.

Energy is a distinct line worth pricing explicitly now that gas is volatile. A rotomolding oven burning 25 to 40 therms per hour at 1.20 USD per therm costs 30 to 48 USD per oven-hour, and a single part cycle draws a share of that based on how many molds share the oven. For a two-mold arm on a 48-minute heat plus servicing window, energy can add 1.50 to 3.00 USD per part. Estimators who fold this into a flat overhead percentage lose money when gas spikes, because oven-heavy thick-wall parts subsidize thin-wall parts unfairly.

Scrap and rework quietly erode margin and belong in the quote as a factored uplift, not an afterthought. Rotomolding first-pass yield commonly sits at 90 to 96 percent, so a 5 percent scrap rate on a 25 USD cost part adds 1.25 USD to every good part shipped. Rework of trimming, patching, or re-spraying carries its own labor. The Scrap/Rework Cost calculator converts your scrap percentage and rework minutes into a per-good-part adder; quoting at target yield instead of actual yield is one of the fastest ways to underbid a job by 5 to 8 percent.

Tooling amortization decides whether a low-volume job is even viable. A fabricated aluminum rotomold can cost 8,000 to 60,000 USD, and spreading it over volume changes the picture completely. A 30,000 USD mold over 500 parts adds 60 USD each, but over 10,000 parts it is 3 USD. Decide up front whether tooling is customer-owned, amortized into piece price, or split, and state it on the quote. Never bury a five-figure tool inside a per-part number without showing the volume assumption, because the buyer will benchmark your piece price against a different quantity.

Overhead and margin sit on top of the built-up cost, and the order matters. Sum material, machine, labor, energy, and scrap into a factory cost, apply overhead at 12 to 25 percent for facility, QA, and indirect labor, then add target margin of 15 to 30 percent. For our tank: 12.50 material + machine share + 4.50 labor + energy + scrap uplift might reach a 34 USD factory cost, 40 USD after overhead, and 50 to 52 USD quoted. Finished Part Cost and Resin Cost Per Part let you rebuild this stack fast when a customer pushes back on price.

Most rotomolding estimates go wrong in three predictable places. First, wall thickness assumptions: quoting a 5 mm nominal wall while production runs 6 mm to hit strength adds 20 percent resin nobody costed. Second, cycle optimism: assuming a 45-minute cycle that runs 54 in reality cuts shift output and raises per-part machine cost. Third, ignoring venting and additive dosing as minor. Re-quote whenever resin moves more than 0.10 USD per kg, gas moves 15 percent, or scrap trends above your quoted rate, and keep the calculator inputs identical to what the floor actually runs.

Published 2026-07-01.