คู่มือนี้ยังไม่ได้แปลเป็นภาษาของคุณ — กำลังแสดงฉบับภาษาอังกฤษ
A purchase order (PO) works a little differently from the other documents in an invoicing workflow, because it's typically the client who issues it, not you. Understanding what it represents helps you use it correctly when one shows up.
What a purchase order actually is
A PO is the buyer's internal authorization to make a purchase — their own commitment, issued to you as the seller, confirming what they're ordering, at what price, and (often) referencing an internal budget or cost center. For businesses with a formal procurement process, it's the document that gets approved before any money can move.
When you'll receive one
Larger or more process-driven clients often issue a PO after accepting your quote or estimate, before work begins — it's their side's paperwork, running parallel to yours. Not every client uses POs; smaller businesses and individual clients often skip this step entirely and go straight from an accepted quote to work starting.
What to do with a PO number
Once a client gives you a PO number, reference it on your invoice. Many companies' accounts-payable departments will not process — or even accept — an invoice that doesn't cite a valid PO number, since it's how their system matches the invoice to an already-approved expense. Leaving it off is one of the most common reasons an otherwise correct invoice gets bounced back.
If you need to issue one yourself
If your own business buys materials or services from vendors or subcontractors, you can issue POs the same way your clients issue them to you — formalizing what you're ordering, at what price, before the vendor starts work or ships goods. Our purchase order generator covers this use case directly.
Purchase order vs. invoice
It's easy to conflate the two since both list items and prices — but they're issued by opposite sides of the transaction, at different points in the process. See our guide on purchase order vs. invoice for the distinction.
A PO isn't paperwork for its own sake — for clients who use them, it's the actual internal green light that makes payment possible. Treating a PO number as optional information is how invoices end up stuck in someone's queue for reasons that have nothing to do with the work itself.