Overview
P_8A is the unit of measure for a line item (in Polish, "miara"). It sits inside each FaWiersz block and describes what one unit of the quantity in P_8B means — pieces, hours, kilograms, a flat fee, and so on.
P_8A is optional. Many invoices leave it out entirely and are perfectly valid, because the XSD does not require a unit label. When you do include it, keep it short and unambiguous: "pcs.", "hrs.", "kg", "m2", or "month" all work. The value is a text field (TZnakowy), so there is no predefined list of units to conform to.
The reason P_8A exists is readability and auditability. If a line says quantity 2 and unit net price 150.50, the buyer cannot tell whether they paid for 2 hours, 2 days, or 2 units of something. Adding "hrs." turns an ambiguous number into a clear billing statement. For a SaaS invoice, "pcs." or "month" is usually the right label; for services billed hourly, "hrs." is the natural choice.
P_8A does not participate in any arithmetic. The invoice totals are computed from P_8B (quantity) and P_9A (unit net price), and the VAT from P_12. A wrong or missing P_8A therefore cannot change the amount due — it only changes how easily the line can be understood. That said, keep P_8A consistent within an invoice: mixing "hrs." and "hours" on different lines is sloppy and confuses reconciliation.
In Notaly you send the unit as the unit property of a line item, and Notaly maps it to P_8A. If you omit unit, the generated XML simply has no P_8A on that line, which is valid. The API does not reject a missing unit because it is not a required field.
A complete, valid FA(3) example appears below, with P_8A filled on both lines.
<Faktura xmlns="http://crd.gov.pl/wzor/2025/06/25/13775/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<Naglowek>
<KodFormularza kodSystemowy="FA (3)" wersjaSchemy="1-0E">FA</KodFormularza>
<WariantFormularza>3</WariantFormularza>
<DataWytworzeniaFa>2026-10-12T07:23:07Z</DataWytworzeniaFa>
<SystemInfo>einvoice-api</SystemInfo>
</Naglowek>
<Podmiot1>
<DaneIdentyfikacyjne><NIP>2745013933</NIP><Nazwa>Example Sp. z o.o. (FICTIONAL)</Nazwa></DaneIdentyfikacyjne>
<Adres><KodKraju>PL</KodKraju><AdresL1>ul. Testowa 1, 00-001 Warszawa</AdresL1></Adres>
</Podmiot1>
<Podmiot2>
<DaneIdentyfikacyjne><NIP>1234563218</NIP><Nazwa>Test Customer S.A. (FICTIONAL)</Nazwa></DaneIdentyfikacyjne>
<Adres><KodKraju>PL</KodKraju><AdresL1>ul. Probna 2, 30-001 Kraków</AdresL1></Adres>
<JST>2</JST>
<GV>2</GV>
</Podmiot2>
<Fa>
<KodWaluty>PLN</KodWaluty>
<P_1>2026-10-12</P_1>
<P_2>FV/2026/10/001</P_2>
<P_13_1>1000.00</P_13_1><P_14_1>230.00</P_14_1>
<P_13_2>301.00</P_13_2><P_14_2>24.08</P_14_2>
<P_15>1555.08</P_15>
<Adnotacje>
<P_16>2</P_16><P_17>2</P_17><P_18>2</P_18><P_18A>2</P_18A>
<Zwolnienie><P_19N>1</P_19N></Zwolnienie>
<NoweSrodkiTransportu><P_22N>1</P_22N></NoweSrodkiTransportu>
<P_23>2</P_23>
<PMarzy><P_PMarzyN>1</P_PMarzyN></PMarzy>
</Adnotacje>
<RodzajFaktury>VAT</RodzajFaktury>
<FaWiersz>
<NrWierszaFa>1</NrWierszaFa>
<P_7>SaaS subscription - October</P_7>
<P_8A>pcs.</P_8A>
<P_8B>1</P_8B>
<P_9A>1000.00</P_9A>
<P_11>1000.00</P_11>
<P_12>23</P_12>
</FaWiersz>
<FaWiersz>
<NrWierszaFa>2</NrWierszaFa>
<P_7>Support</P_7>
<P_8A>hrs.</P_8A>
<P_8B>2</P_8B>
<P_9A>150.50</P_9A>
<P_11>301.00</P_11>
<P_12>8</P_12>
</FaWiersz>
</Fa>
</Faktura>Sources
Source: crd.gov.pl