# PEPPOL-EN16931-R130: Use the line quantity unit on the price base quantity

When `cac:Price/cbc:BaseQuantity` has a `unitCode`, it must be the code used on the line quantity. Convert the price rather than relabel the unit.

- Layer: Peppol BIS Billing
- Severity: fatal (the document is invalid)
- Topics: Lines and prices, Code lists
- Official definition: https://docs.peppol.eu/poacc/billing/3.0/rules/ubl-peppol/PEPPOL-EN16931-R130/
- Explanation last updated: 2026-09-24

## The short answer

`PEPPOL-EN16931-R130` fails when `cac:Price/cbc:BaseQuantity` has a `unitCode` other than the one on the line quantity. In the recorded example the quantity is in `C62` and the base quantity in `H87`. Give the base quantity the unit of the quantity, and if the price was quoted in another unit, restate the price and base quantity in the quantity unit.

Each code can be valid on its own; what fails is the disagreement. `C62` (one) and `H87` (piece) are both on the unit list, which is why the EN 16931 layer passes.

## What the rule checks

The rule runs on each `cbc:BaseQuantity` that has a `unitCode` attribute and compares that code with the `unitCode` of the quantity on the same line: `cbc:InvoicedQuantity` in an invoice, `cbc:CreditedQuantity` in a credit note.

The comparison is a plain match of the two strings, with no unit conversion and no case folding. When tried, `c62` against `C62` failed here and under `BR-CL-23`, and `unitCode=" C62 "`, with spaces around the code, failed here alone.

Three situations are skipped. A base quantity with no `unitCode` is not checked; removing the attribute from the recorded base quantity gave a clean result when tried. A line with no quantity element is left alone, and `BR-22` reports it. A line with no `cbc:BaseQuantity` has nothing to compare.

A quantity that exists without a `unitCode` still counts as a quantity, so a base quantity that has a unit fails against it. That is why a missing line unit reports this rule next to `BR-23`.

| Term | Meaning | UBL element |
|---|---|---|
| BT-150 | Item price base quantity unit of measure code | `cac:InvoiceLine/cac:Price/cbc:BaseQuantity/@unitCode` |
| BT-130 | Invoiced quantity unit of measure code | `cac:InvoiceLine/cbc:InvoicedQuantity/@unitCode (cac:CreditNoteLine/cbc:CreditedQuantity/@unitCode in a credit note)` |
| BT-149 | Item price base quantity | `cac:InvoiceLine/cac:Price/cbc:BaseQuantity` |

## How an integration ends up here

Possible causes, from the shape of the rule rather than from measured usage:

- The price comes from a price list kept per kilogram, per metre or per pack, while the quantity is recorded in grams, centimetres or single items.
- Two mapping tables translate units, one for order or delivery lines and one for the price list, and they give the same local unit different codes, such as `C62` in one and `H87` in the other.
- The base quantity unit is fixed in the template while the line unit comes from the product.
- The line unit was corrected after a `BR-CL-23` finding and the base quantity kept the old code.

## How to fix it

1. Compare the two `unitCode` values on the failing line and decide which unit the quantity is really counted in. The quantity unit describes what was delivered, so keep it unless it is itself the wrong one.
2. If both codes mean the same thing to you, such as `C62` and `H87` for single items, pick one and write it on both elements. Make the unit mapping produce a single code for each local unit.
3. If the price is quoted in a different unit, express the base quantity in the line unit. A price of 50 per kilogram against a quantity of 500 grams becomes a price of 50 for a base quantity of 1000 `GRM`. When tried, that line with a net amount of 25.00 passed every layer.
4. Do not only relabel the unit. `PEPPOL-EN16931-R120` ignores units and divides the price by the base quantity as a plain number: when tried, the same line with the price per 1 `KGM` failed that rule too, because 500 x 50 is not 25.00, and writing `GRM` over a base quantity of 1 would leave that gap in place.
5. Leaving `unitCode` off `cbc:BaseQuantity` also passes, because the rule then has nothing to compare, but writing the same code as the quantity keeps the price self-describing.

## Before and after

These are fragments, not complete documents. The complete synthetic documents they come from are linked below.

Fragment of the failing invoice: the quantity is in C62, the price base quantity in H87

```xml
<cac:InvoiceLine>
  <cbc:ID>1</cbc:ID>
  <cbc:InvoicedQuantity unitCode="C62">2</cbc:InvoicedQuantity>
  <cbc:LineExtensionAmount currencyID="GBP">25.00</cbc:LineExtensionAmount>
  <!-- item omitted from this fragment -->
  <cac:Price>
    <cbc:PriceAmount currencyID="GBP">12.5</cbc:PriceAmount>
    <cbc:BaseQuantity unitCode="H87">1</cbc:BaseQuantity>
  </cac:Price>
</cac:InvoiceLine>
```

Fragment of the corrected invoice: both quantities are in C62

```xml
<cac:InvoiceLine>
  <cbc:ID>1</cbc:ID>
  <cbc:InvoicedQuantity unitCode="C62">2</cbc:InvoicedQuantity>
  <cbc:LineExtensionAmount currencyID="GBP">25.00</cbc:LineExtensionAmount>
  <!-- item omitted from this fragment -->
  <cac:Price>
    <cbc:PriceAmount currencyID="GBP">12.5</cbc:PriceAmount>
    <cbc:BaseQuantity unitCode="C62">1</cbc:BaseQuantity>
  </cac:Price>
</cac:InvoiceLine>
```

Only the `unitCode` of `cbc:BaseQuantity` differs: `H87` in the failing invoice, `C62` in the corrected one, matching `cbc:InvoicedQuantity`. The failing document reports only `PEPPOL-EN16931-R130`. `H87` is a recognised unit, so `BR-CL-23` stays quiet, and the line calculation does not look at units, so `PEPPOL-EN16931-R120` still finds 2 x 12.5 = 25.00.

### What the validator reported

- The failing invoice reports **PEPPOL-EN16931-R130**. The corrected document passes every layer with no findings.
  - [Download the failing XML](https://ironfang.uk/finance/rule-examples/PEPPOL-EN16931-R130-invalid.xml)
  - [Download the corrected XML](https://ironfang.uk/finance/rule-examples/invoice-minimal.xml)

Recorded on phive 12.1.0 / phive-rules-peppol 4.5.6 / Saxon-HE 12.10, the engine behind the free validator, using synthetic data. A recorded result is regression evidence for these documents; it is not a certification.

## Where it applies

- Applies to UBL `Invoice` and `CreditNote`. In a credit note the comparison is with `cbc:CreditedQuantity`; when tried, a credited quantity in `C62` against a base quantity in `H87` reported this rule alone, as on the invoice.
- This is a Peppol BIS rule, reported on the Peppol layer. The EN 16931 layer does not report the mismatch: it passes in the recorded example.
- An unrecognised code on either element is a separate finding, `BR-CL-23`, and the two rules can be reported together for the same base quantity.

## Related rules

- [BR-23 requires the unit code on the line quantity that this rule compares against](https://ironfang.uk/docs/finance/rules/BR-23.md)
- [BR-CL-23 checks that each unit code is a recognised UN/ECE code](https://ironfang.uk/docs/finance/rules/BR-CL-23.md)
- [PEPPOL-EN16931-R121 requires the price base quantity itself to be above zero](https://ironfang.uk/docs/finance/rules/PEPPOL-EN16931-R121.md)
- [PEPPOL-EN16931-R120 divides the price by the base quantity when it checks the line net amount](https://ironfang.uk/docs/finance/rules/PEPPOL-EN16931-R120.md)

## Scope and source

Written for Peppol BIS Billing 3.0.21 (May 2026), EN 16931 1.3.16, as applied to UBL 2.1 Invoice and CreditNote documents. Other profiles, syntaxes and releases can define this identifier differently. Guidance version 2026-09-24.1: source checked 2026-09-24, explanation last updated 2026-09-24.

[The official definition of PEPPOL-EN16931-R130](https://docs.peppol.eu/poacc/billing/3.0/rules/ubl-peppol/PEPPOL-EN16931-R130/) carries the normative wording and test. This page is our explanation of it, not a copy.

Guidance does not change the engine verdict. Fixing this finding does not mean the document passes every layer, and validation does not certify legal or tax compliance or transmit a document over Peppol.

## Links

- [This rule as a web page](https://ironfang.uk/docs/finance/rules/PEPPOL-EN16931-R130)
- [Free Peppol invoice validator](https://ironfang.uk/tools/peppol-validator)
- [Rule index](https://ironfang.uk/docs/finance/rules.md)
- [Ironfang Finance API docs](https://ironfang.uk/docs/finance)
- The same rule is available to MCP clients as the tool `finance.rule.get` on https://mcp.ironfang.uk/mcp