Unit of Measure (UoM) – Conversion & ConsistencyGlossary

Unit of Measure (UoM) – Conversion & Consistency

Q: What rounding mode should we use?

Choose and document a default (e.g., half-up or half-even) and exceptions by use case (label display vs internal calc). Store raw values at higher precision than display to avoid cumulative rounding error.

Q: How do we express active ingredient vs gross weight?

Capture potency and loss-on-drying/moisture as attributes; dose and report in active units where required, while maintaining gross weights for material management.

This topic is part of the SG Systems Global regulatory & operations glossary.

Updated October 2025 • Master Data, Weights & Measures • Manufacturing, Quality, Warehouse, Laboratory

Unit of Measure (UoM) is the controlled vocabulary and conversion logic that makes quantities unambiguous across purchasing, production, testing, labeling, and distribution. A robust UoM model defines a canonical unit per item (e.g., kilograms for an excipient, milliliters for a solvent, each for a device), governs alternative units (g, mg; L, mL; box, case, pallet), and enforces exact conversions and rounding rules in every system where quantities are created or consumed—MES, LIMS, WMS, ERP, and labeling. Done well, UoM turns a web of numbers into a single source of truth for recipes, BOMs, CoAs, and shipping documents.

“One product, one truth: UoM is the grammar that makes every quantity say exactly what you mean—every time, in every system.”

TL;DR: Assign a canonical UoM per item and a governed set of alternates with exact conversion factors, effective dates, and rounding modes. Separate dimensional families (mass, volume, count, concentration); allow mass↔volume only via controlled density references; apply tare for net weight; gate conversions through validated engines (CSV) with audit trails, Part 11/Annex 11 controls, and Document Control. Keep labels, barcodes, and GS1 GTIN/SSCC aligned with pack UoMs.

1) What UoM Covers—and What It Does Not

Covers: definition and governance of base and alternate units; dimensional consistency (mass, volume, count, length, area, time, temperature, concentration such as %w/w, %w/v, mg/mL, IU); conversion factors and effective dates; rounding and significant figures; gravimetric vs volumetric logic; density and potency references for cross‑dimension conversions; pack hierarchies (each→box→case→pallet) and their counts; interface mappings to EDI/labels and warehouse moves.

Does not cover: UoM governance cannot “fix” bad specifications, mislabeled artwork, or poor recipe formulation. It also does not replace calibration, MSA, or training; those ensure measurements are accurate before units are applied.

2) Legal, System & Data Integrity Anchors

Because units show up on labels, CoAs, and release documentation, UoM settings must live under controlled SOPs with versioning and approvals in Document Control. Electronic conversions and unit displays fall within Part 11/Annex 11 expectations and should be validated proportionately under CSV. Metrology references (e.g., density tables) should trace to authoritative sources (e.g., NIST). All calculations and changes must be attributable and reconstructable via audit trails, with retention per Record Retention.

3) The Evidence Pack for UoM Control

An audit‑ready packet includes: the item’s canonical UoM; allowed alternates and conversion factors; dimensional family; rounding/significant‑figure rules; label abbreviations; pack hierarchy and counts (EA/BOX/CASE/PAL); density or potency references with version and temperature range; tare definitions for containers and dunnage (Tare Weight); test results showing correct conversions in the eBMR/LIMS/WMS; and cross‑system mappings (ERP, EDI, labels, reports). Store approvals and changes under MOC.

4) From Master Data to Execution—A Standard Path

Start at item creation: pick a canonical UoM aligned to how the material is controlled and released. Define alternates and pack levels with exact factors and effective dates. At Goods Receipt, convert supplier UoM into canonical and capture pack metadata. During dispensing and batching, the MES enforces UoM on setpoints and targets (Master Recipes); balances and flowmeters report in device units and the system converts with governed rounding. LIMS results are recorded in method UoM and displayed to specifications in release UoM with traceable transformations. WMS uses the same catalogue to move, count, and label inventory consistently across locations and documents.

5) Cross‑Dimension Conversions—Density & Potency

Mass↔volume conversions require a controlled density (and often temperature) reference—either standard curves for a solvent or a lot‑specific value from testing. Similarly, conversions from “material quantity” to “label claim” require potency (% assay, water content, IU) so the MES can dose active rather than gross weight. Treat both density and potency as master‑data attributes with effective dating and link them to the batch’s calculations and labels.

6) Weighing, Tare & Device Resolution

UoM correctness depends on accurate net quantity. Define container tares in master data, enforce on the shop floor, and record evidence in the eBMR (Gravimetric Weighing, Tare Weight). Respect device resolution and rounding; configure acceptance windows in the same UoM as the target to avoid silent unit mismatches. If devices report in one unit (e.g., g) while recipes are in another (e.g., kg), conversions must be deterministic and validated.

7) Pack Hierarchies, Labels & Traceability

Define each→box→case→pallet counts and variable‑measure rules where applicable (e.g., random weight). Keep serialization and SSCC aligned to pack UoMs; labels should show the correct unit and quantity with barcode verification. For downstream traceability and EPCIS events, pack UoMs must match the EPCIS quantity semantics and EDI unit codes used by trading partners.

8) Regulatory Labeling & Claims

Nutrition, dosage strength, and cosmetic claims are unit‑sensitive (e.g., mg/mL, %w/w, IU per dose). Align method UoM, specification UoM, and label artwork under Labeling Control. Ensure rounding logic does not misstate claims; where regulations prescribe display units (e.g., per serving under 21 CFR Part 101), the system must convert and format consistently, with evidence in the batch record and label approval files.

9) Rounding, Significant Figures & Display

Define and govern rounding (half‑up vs half‑even), precision per characteristic, and display rules distinct from stored precision. Store raw values at high precision; display per SOP. Always show the unit with the value in records, labels, and reports. In SPC and CPV contexts, keep a single unit per chart to avoid false signals due to conversion artifacts.

10) UoM in SPC, Capability & CPV

Control limits and capability indices assume a consistent unit. Normalize measurements to a governed analysis UoM before charting; document the conversion in the chart metadata and Control Plan. Changing units mid‑stream invalidates historical limits; treat as a controlled change and re‑establish baselines (CPV).

11) Inventory, FEFO & Costing

WMS and ERP require unit‑consistent quantities for reservations, picks, and Pack & Ship. FEFO logic needs the same unit the lot’s expiry and balance are tracked in. Costing and yield calculations rely on canonical units to compare planned vs actual; mixing units hides loss or gain and undermines KPIs.

12) Metrics That Demonstrate Control

UoM discrepancy rate: number of transactions blocked for unit mismatch per 1,000 transactions.
Label/UoM correction count: changes to labels or CoAs due to unit errors.
Rounding exception rate: instances where rounding altered pass/fail status.
Density/potency currency: % of lots with current references applied in MES/LIMS.
Cross‑system alignment: % of items with identical UoM sets across MES/LIMS/WMS/ERP.

Together, these indicate whether conversions are governed and trustworthy from receipt to release and shipment.

13) Common Pitfalls & How to Avoid Them

Free‑text units. Use a controlled catalogue; block ad‑hoc entry.
Hidden cross‑dimension jumps. Require explicit density/potency references for mass↔volume or gross↔active conversions.
Pack factor drift. Treat pack count changes as MOC with label review.
Device vs recipe units. Validate device‑to‑recipe conversions and rounding; don’t rely on operator mental math.
Display vs storage precision. Store high‑precision; display per SOP to prevent rounding‑induced OOS/OOT confusion.
Partner code mismatches. Maintain maps between internal units and partner EDI/EPCIS codes; test in integration.

14) What Belongs in the UoM Record

Record the canonical unit, alternates and exact factors, dimensional family, rounding and display rules, label abbreviations, pack hierarchy and counts, density/potency references (source, temperature range), tare definitions, validation evidence for conversions, cross‑system code maps, and all approvals/changes with reasons and effective dates. Keep links to impacted recipes, labels, specifications, and training under Document Control.

15) How This Fits with V5 by SG Systems Global

Unified UoM catalogue. The V5 platform maintains a single, versioned UoM catalogue shared by MES, LIMS, WMS, and labeling. Items select a canonical unit and an allowed set of alternates; conversions are effective‑dated and governed with approvals and audit trails.

Deterministic conversion engine. V5’s validated engine performs all conversions server‑side with traceable math, rounding per SOP, and dimensional checks that prevent illegal conversions. Mass↔volume requires linked density references; gross↔active requires potency—both versioned and tied to lots and methods.

Shop‑floor & lab enforcement. In MES, recipe setpoints, tolerances, and device readings are normalized to the item’s analysis unit, removing manual conversion risk. In LIMS, result entry and specification display units are enforced, with clear provenance between stored and displayed values.

Pack hierarchies & labels. V5 models EA/BOX/CASE/PAL with counts and random‑weight rules; Label Verification and EPCIS events use the same units, ensuring GTIN/SSCC alignment from unit to pallet.

Integration without drift. V5 maps internal units to partner EDI codes and validates payloads at the boundary so quantities and units stay consistent across suppliers and customers. Changes to maps are controlled under MOC and tested under CSV.

Bottom line: V5 turns UoM from tribal knowledge into governed, testable logic—so every gram, milliliter, and “each” means the same thing everywhere.

16) FAQ

Q1. Can we convert between mass and volume?
Yes, but only with a controlled density reference (and temperature where relevant). Treat density as master data with versioning and apply it automatically in MES/LIMS; document the calculation path in the record.

Q2. How should we handle supplier UoMs that differ from ours?
Receive in supplier UoM but convert to the item’s canonical unit at receipt using the governed catalogue. Store both for traceability and reconcile pack counts to internal hierarchies.

Q3. What rounding mode should we use?
Choose and document a default (e.g., half‑up or half‑even) and exceptions by use case (label display vs internal calc). Store raw values at higher precision than display to avoid cumulative rounding error.

Q4. How do we express active ingredient vs gross weight?
Capture potency and loss‑on‑drying/moisture as attributes; dose and report in active units where required, while maintaining gross weights for material management.

Q5. What about odd pack units (dozen, gross) or random weight?
Model them explicitly with exact factors (12, 144) or random‑weight rules tied to weighed net content. Do not allow free text.

Q6. Do device units have to match recipe units?
Not necessarily, but conversions must be enforced and validated. Prefer aligning device configuration to recipe units to reduce complexity; where not possible, let MES perform deterministic conversions with audit trails.