---
alias: user-guide-material-quantity-unit-changes
description: "This documentation explains how unit conversions are handled during material processing steps"
---

# Material Quantity Unit Changes

Critical Manufacturing MES always tracks a primary quantity, and optionally a secondary quantity, for every **Material**. The primary and secondary units are stored at the **Material** level, but are defined at the **Step** level. A **Step** can define whether it defines the units with the property Set Units or not. If a **Step** does not define the units, when a **Material** arrives at that **Step**, it maintains its units. When a **Material** is moved to a **Step** that defines units, the quantities are preserved if the units are the same, otherwise the table below applies for converting the quantities to the new units. The conversion factors are defined at the Product level in the Unit Conversion Factors.

!!! note
	Unit Conversion Factors work in both directions, that is, if Product 1 defines a conversion factor from Unit A to Unit B as being 5, if the system is looking for the reverse conversion factor (Unit B to Unit A) and it does not exist, it assumes the inverse of the conversion from Unit A to Unit B, in this case 0.2.

| Scenario | Units | Old Step | New Step | Result | Applied conversion factor | If conversion factor does not exist |
|----------|-------|----------|----------|--------|---------------------------|---------------------------------|
| 1 | Primary | A | A | A quantity remains | 1 (none) | N/A |
| 1 | Secondary | B | - | B quantities are dropped | N/A | N/A |
| 2 | Primary | A | B | B quantity (switched) | 1 (none) | N/A |
| 2 | Secondary | B | - | A quantity is dropped | N/A | N/A |
| 3 | Primary | A | B | B quantity (switched) | 1 (none) | N/A |
| 3 | Secondary | B | A | A quantity (switched) | 1 (none) | N/A |
| 4 | Primary | A | C | C quantity (converted) | A -> C | Exception |
| 4 | Secondary | B | D | D quantity (converted) | B -> D | 0 |
| 5 | Primary | A | C | C quantity (converted) | A -> C | Exception |
| 5 | Secondary | B | A | A quantity (switched) | 1 (none) | N/A |
| 6 | Primary | A | B | B quantity (switched) | 1 (none) | N/A |
| 6 | Secondary | B | D | A quantity (converted) | B -> D | 0 |
| 7 | Primary | A | C | C quantity (converted) | A -> C | Exception |
| 7 | Secondary | B | - | B quantities are dropped | N/A | N/A |
| 8 | Primary | A | C | C quantity (converted) | A -> C | Exception |
| 8 | Secondary | - | - | - | N/A | N/A |
| 9 | Primary | A | C | C quantity (converted) | A -> C | Exception |
| 9 | Secondary | - | D | D quantity (converted) | A -> D | 0 |
| 10 | Primary | A | C | C quantity (converted) | A -> C | Exception |
| 10 | Secondary | - | A | A quantity (switched) | 1 (none) | N/A |
| 11 | Primary | A | A | A quantity remains | 1 (none) | N/A |
| 11 | Secondary | - | B | B quantity (converted) | A -> B | 0 |