Polyethylene (PE) is a semicrystalline thermoplastic produced by high-pressure free-radical polymerization or by low-pressure coordination polymerization over Ziegler-Natta, Phillips, or metallocene catalysts. Quotation units for polyethylene: per tonne, per KG and per grade are not interchangeable; they encode logistics, quantity, and specification severity. A bulk railcar quotation is normally denominated in USD/t or EUR/t, whereas a distributor bag quotation is stated in USD/kg or EUR/kg. A grade-specific contract may price a particular HDPE PE100 pipe compound per tonne with lot-level test certification, thereby combining per-tonne commercial formatting with per-grade technical identity.

Grade identity is defined by density and melt mass-flow rate under ISO 1133-1:2022 and ISO 1183-1:2019. High-density polyethylene pipe grades typically exhibit a density of 0.945–0.965 g/cm³ and an MFR of 0.2–0.5 g/10 min at 190 °C under 2.16 kg. Low-density polyethylene film grades typically exhibit a density of 0.915–0.930 g/cm³. Because the same mass of resin occupies different volumes at different densities, a quotation per kg cannot be translated into a quotation per tonne without confirming the grade and the packaged form.

What Determines Whether Polyethylene Is Quoted Per Tonne or Per KG?

Quotation unit selection is governed by package configuration, transport mode, and metering precision. For polymer resins moving as railcar lots of 50–100 tonnes, bulk silo trucks of 20–25 tonnes, or international container loads of 18–26 tonnes, the standard invoicing unit is per tonne. The bulk quotation includes moisture content limits, pellet dust tolerance, and bulk density range because these parameters alter storage capacity and conveying energy. Under ISO 60:1977 or ASTM D1895-17, bulk density of PE pellets typically falls between 480 kg/m³ and 600 kg/m³ depending on pellet geometry and crystallinity. A load of 25,000 kg at 530 kg/m³ occupies 47.2 m³, which is the working volume basis for silo scheduling and freight planning.

For changes in package configuration, the quotation basis switches to per kg. Distributors supplying 25 kg multiwall bags, 1,000 kg flexible intermediate bulk containers, or 20 kg vacuum-packed sacks use per-kilogram invoicing because the total order is often below one pallet or less than one tonne. The arithmetic conversion from bulk price is price per kg = price per tonne ÷ 1,000. However, small-lot conversion alone does not capture bagging loss, label certification, or surface moisture regain, so the distributor per-kg quotation usually contains a premium over the arithmetic equivalent of a railcar tonne price.

Per Grade Quotation Requires More Than Density and Melt Flow Rate

Grade-based quotation is a contractual mechanism to separate materials that are nominally both polyethylene but differ in copolymer type, molar mass distribution, catalyst residue, and stabilizer package. A C4-butene LLDPE film grade with density of 0.918 g/cm³ and MFR of 1.0 g/10 min is not price-identical to a C8-octene LLDPE grade of the same density and MFR, because hexene or octene comonomer increases production cost and alters dart impact and tear propagation. The quotation per grade therefore includes a base polymer price plus differentials for comonomer type, additive system, and certification protocols. It is normally denominated per tonne for annual contracts and per kg for spot distributor purchases.

The table below summarizes common industrial quotation unit conventions for a non-exhaustive set of PE families, with the test methods used to verify grade identity. The values reflect widely published specification windows in ISO 1872-1:2018 and ASTM D4976-12a, not current market prices.

Quantitative price differences among film grades are region-specific and published data for this specific configuration is limited; however, the per-grade quotation structure remains necessary because comonomer and additive choices change conversion behavior. A processor cannot simply compare two HDPE blow-molding quotations per kg unless both state the same conditions: MFR of 0.35 g/10 min under ISO 1133-1:2022, density of 0.956 g/cm³ under ISO 1183-1:2019, and a minimum bottle impact value under ASTM D2463-15. The absence of any one specification can invalidate the per-kg comparison because a lower density or higher MFR may reduce cycle time but sacrifice environmental stress crack resistance under ASTM D1693-15.

For HDPE injection molding grades with MFR 4.0–12 g/10 min, processing on reciprocating-screw machines with clamp force 2,000–3,000 kN is common for crates, toys, and containers. The per-tonne quotation is generally used at annual volumes above 50 tonnes, while a per-kg trial quotation is used for process validation lots of 500 kg or less. In such a trial, the processor measures melt pressure stability, screw recovery time, and shrinkage under ISO 294-4, and the per-kg price is meaningful only when the grade certificate includes density, MFR, and additive package. Published data on trial-lot price comparisons is limited because regional distributor markups vary; the technical comparison remains valid only under identical test conditions.

When a contract changes from per-tonne bulk to per-kg packaging, the per-kg quote is arithmetically derived but operationally burdened by repackaging and quality assurance. A 1,000 kg flexible intermediate bulk container of HDPE injection grade drawn from a railcar lot may require dried-air purging to below 0.05% moisture before sealing, after which the per-kg price is recalculated to include the amortized cost of a desiccant vent and sack-sealing line. The quotation unit per grade remains the controlling technical identifier: the same per-kg number has no specification meaning unless the grade is identified by density, MFR, comonomer, and additive package. In customs declarations, the statistical unit may be kg under the Harmonized System code 3901.10 for LDPE or 3901.20 for HDPE, while the commercial invoice may state both per-kg and total tonnes for letter-of-credit compliance.

When Bulk Silo Discharge and Loss-in-Weight Feeding Dictate the Unit Basis

In continuous extrusion plants, the unit basis often follows the mass-flow metering configuration. A loss-in-weight hopper calibrated to ±0.2% feed-rate accuracy over 30 s intervals makes per-kg dosing records natural, while the commercial purchasing contract may remain per-tonne. This dual-unit condition is common in high-speed blown film lines where the screw diameter is 65 mm, L/D ratio 30:1, and the throughput is 180–250 kg/h. The per-kg quotation unit is used for internal cost allocation; the per-tonne unit is used for supplier invoicing.

Field data from production-scale equipment show that pellet bulk density variation shifts the relationship between volumetric feeder speed and mass output. If a silo contains LLDPE with a bulk density of 510 kg/m³ and the feeder screw is set for a specific volume per revolution, the same setting will not deliver the same mass rate as a grade with a bulk density of 570 kg/m³. The discrepancy enters the per-kg cost calculation because the extruder consumes mass, not volume, but the feeder is volumetric. For this reason, grade-specific quotations often include a bulk density range and pellet size distribution under ASTM D1921-18 or equivalent.

In blown film extrusion of LLDPE, a per-kg quotation is frequently paired with a per-tonne freight adjustment because a single three-layer line with die diameter 250 mm and die gap 1.8 mm may consume 8–12 tonnes/day. The per-grade specification includes melt strength, draw-down ratio, and coefficient of friction under ISO 8295. The use of C6 or C8 comonomer affects the per-kg price not because of density alone, but because the longer comonomer alters polymer architecture and downstream film tensile properties. Published data for the exact price differential among C4, C6, and C8 LLDPE in a specific region is limited; however, the per-grade quotation separates those costs as explicit comonomer premiums.

If the Quotation Unit Is Per KG for Specialty Polyethylene

Specialty PE grades such as crosslinkable high-pressure LDPE for power-cable insulation, LLDPE rotational molding powder, and UHMWPE are typically quoted per kg rather than per tonne because order quantities are often 500–5,000 kg and the material requires additional testing. A crosslinkable LDPE compound containing dicumyl peroxide at 1.8–2.2 wt% is quoted per kg with a maximum storage temperature of 25 °C and a shelf life of 6 months when sealed in 20 kg moisture-barrier bags. The per-kg unit supports lot-level traceability to the peroxide masterbatch and avoids the bulk-handling risk of premature scorch. Dicumyl peroxide exhibits a 10-hour half-life near 117 °C; therefore, the compound is processed at melt temperatures below 125 °C and crosslinked at 180–200 °C in continuous catenary lines.

UHMWPE powder for ram extrusion or compression molding is also sold on a per-kg basis because each grade is differentiated by viscosity number or molar mass rather than MFR. Under ISO 11542-1:2001, UHMWPE is designated by viscosity number greater than 1,500 mL/g; under ASTM D4020-18, the molar mass may be specified by the intrinsic viscosity method. A quotation per grade for UHMWPE typically lists the viscosity number, density, residual catalyst content as ash below 0.02%, and particle size distribution, and the per-kg price is calculated from the full batch certificate rather than a simple bulk polymer price.

LLDPE rotational molding powder quoted per kg may be specified as 35-mesh powder with dry flow under ASTM D1895-17. Powder grades differ from pellet bulk pricing because pulverization adds energy input of approximately 0.1–0.2 kWh/kg and reduces bulk density to 420–480 kg/m³. The per-kg quotation therefore includes particle-size distribution, dry flow, and the energy cost of size reduction, while the per-tonne quotation for the same resin in pellet form would not include these items.

Regulatory compliance also interacts with quotation units. Food-contact grades under FDA 21 CFR §177.1520 are commonly quoted per tonne with an additional certification line item per grade, because the certificate of compliance must be traceable to lot number, resin producer, and converter. A grade with a heavy-metal migration certificate under REACH Article 33 and residual monomer below detection limits may be quoted per kg for laboratory and pilot-scale orders. Published data for regional price differentials caused by compliance documentation is limited; however, the quotation structure generally separates the polymer cost per tonne or kg from the cost of documentation per grade.

Polyethylene itself is not hydrolytically sensitive, but surface moisture on pellets under RH >60% can produce bubbles in thick-wall extrusion; pre-drying at 70–80 °C for 2–4 hours may be used for film or pipe when visual defects appear. For wire-and-cable formulations, copper contact requires a metal deactivator because exposed copper accelerates thermo-oxidative degradation. These operational boundaries are part of the per-grade quotation because a material that passes the same density and MFR specification can fail a process audit when the additive package is not matched to the conversion line.