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What Is a Purchase Order (PO)? Meaning and Example

A purchase order is a buyer's document that authorises a purchase. Learn what it contains, where the PO number goes on an invoice and how it differs from a quote.

Glossary · 1 min read · Updated 2 October 2026

By the Invoicelywise editorial team

Definition

A document a buyer sends to a seller to order goods or services at agreed prices. The PO number is then quoted on the seller's invoice.

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On this page
  1. What it usually contains
  2. Where it fits in the flow
  3. Why the PO number matters on an invoice
  4. Using this site

A purchase order, or PO, is a document a buyer sends to a seller to order goods or services at agreed prices and terms. It authorises the purchase, and it carries a PO number that both sides use to match the order, the delivery and the invoice.

What it usually contains

  • The buyer’s and seller’s details and the PO number.
  • A list of items or services with quantities and agreed prices.
  • Delivery details and the expected date.
  • Payment terms and the total.

Where it fits in the flow

  1. The seller sends a quote.
  2. The buyer accepts and issues a purchase order.
  3. The seller delivers the goods or does the work.
  4. The seller sends an invoice that quotes the PO number.
  5. The buyer matches the invoice to the PO and pays.

Why the PO number matters on an invoice

Large organisations often match each invoice to a PO before they release payment. An invoice without the number can be rejected or delayed. On this site’s invoice generator, put the PO number in the notes field, for example “PO: 4512”.

Using this site

This site’s tools do not issue purchase orders, because the buyer issues them. If a client gives you a PO number, add it to the notes of your invoice. For what else belongs on an invoice, see what to include on an invoice.

General information, not legal or tax advice. Rules differ by country.

Frequently asked questions

Do I need a PO number on my invoice?

If the client gave you one, include it. Many companies will not pay an invoice without it. Put it where the client's finance team will see it. On this site, that means the notes field, as there is no separate PO field.

What is the difference between a quote and a purchase order?

A quote is the seller's offer with prices. A purchase order is the buyer's order, usually placed after accepting a quote.

Invoice generatorCreate an invoice and download it as a PDF.Quote generatorSend a price quote the client can accept.Credit noteA document a seller issues to reduce or cancel part or all of an invoice already sent, for a return, a correction or a discount.Pro forma invoiceA preliminary document that states what you will charge before the work is done or the goods are shipped. It can be used to request an advance payment, but it is not the final invoice or a tax record.Invoice vs Receipt vs Quote vs Estimate: What Is the Difference?Four documents that look alike but do different jobs. Learn when to send a quote, an estimate, an invoice or a receipt.What to Include on an Invoice (Required vs Optional)A plain-language checklist of what an invoice usually must contain, what is optional, and why requirements differ by country.