A purchase order, or PO, is the buyer’s formal request to a supplier to provide goods at an agreed price and quantity. Once the supplier accepts it, it becomes a binding contract. It is the document that turns “we need to reorder” into an auditable commitment, and it is where procurement and inventory management connect.
What a purchase order contains
A complete PO removes ambiguity from the transaction. The essentials:
- PO number for tracking and matching later.
- Buyer and supplier details.
- Line items: SKU, description, quantity, and agreed unit price.
- Delivery date and location.
- Payment terms.
- Totals, including any tax and shipping.
The line-item detail matters because it is what receiving and accounts payable later match against.
How the workflow runs
- Need identified. A reorder point triggers, or a buyer raises a requisition. This is where stock replenishment hands off to procurement.
- PO created and approved. The buyer issues the PO; internal approval gates large orders.
- Supplier accepts. Acceptance makes it a binding order.
- Goods received. The warehouse books the receipt against the PO, updating inventory control.
- Three-way match. Accounts payable matches the PO, the receiving record, and the supplier invoice before paying. Mismatches are caught here, not after the money has gone.
Why the PO matters for inventory
A PO is not just a buying document; it is an inbound stock signal. Open POs tell you what is on the way and when, which is exactly what an available-to-promise calculation and a forward-looking stock position need. Without POs in the system, you are planning against on-hand alone and will be surprised by both arrivals and shortfalls.
Purchase order vs invoice
They are easy to confuse. The buyer issues the purchase order to start the transaction; the supplier issues the invoice to request payment for it. The PO comes first and states what was ordered; the invoice comes after delivery and states what is owed. The three-way match exists precisely to confirm the two agree with what was actually received.
Getting POs right
Use sequential PO numbers, require approval thresholds, and book receipts against the PO promptly so the three-way match works and your inbound stock picture stays accurate. Done well, the humble purchase order is the control point that keeps purchasing, receiving, and payment honest.