PO Number: What It Is and How to Use It

A PO number (purchase order number) is the unique reference a buyer gives to each purchase order it issues. The supplier quotes that number on its order confirmation, delivery note, packing list and invoice, so the buyer's accounts team can match every document to the order and approve payment.

Where the PO number goes

• On the purchase order itself, near the top, with the date. Create one with the purchase order generator.
• On the supplier's invoice, usually in a "PO number" or "your reference" field. Many large buyers reject or hold invoices that do not show a valid PO number.
• On shipping documents: the packing list, the commercial invoice and often the carton marks, so the receiving warehouse can book the goods in.

What does a PO number look like?

There is no standard format; each buyer chooses its own. Common patterns are a prefix, a year and a running number, sometimes with a site or department code:

Format	Example
Running number	4500018732
Prefix and year	PO-2026-0147
Site and number	KHI/PO/00382

Whatever the format, each number should be used once only, so a document can never match two orders.

How three way matching works

Before paying, many accounts teams match three documents: the purchase order (what was ordered and at what price), the goods receipt (what actually arrived) and the supplier's invoice (what is being charged). The PO number links them. If quantities or prices differ, the invoice is held until the difference is resolved, which is the most common cause of late supplier payments.

PO number vs invoice number

The buyer creates the PO number; the seller creates the invoice number. An invoice therefore normally carries both. One purchase order can lead to several invoices if it is delivered in parts, and each invoice should still show the same PO number. See purchase order vs invoice for the full comparison.