What Is a Purchase Order? How POs Work, With Examples
A purchase order (PO) is a document a buyer sends to a supplier to authorise a purchase. It states what is being bought, how much, at what price and on what terms. Once the supplier accepts it, the PO becomes the reference point for delivery, invoicing and payment.
POs are easy to dismiss as corporate paperwork, but they solve a real problem. They record what was agreed before any money or goods move, which is exactly the moment misunderstandings are cheapest to fix.
What is a purchase order?
A purchase order is the buyer's side of a transaction written down in advance. Where a quote is the supplier saying "this is what we'll charge", the PO is the buyer saying "we accept, please supply exactly this". It gives the purchase an internal approval trail, and the supplier something concrete to deliver against.
For the buyer, an approved PO is also a commitment to spend. Recording it lets a business see money that is promised but not yet invoiced, which is useful when forecasting cash flow.
What should a purchase order include?
| Field | Why it matters |
|---|---|
| PO number | The unique reference the supplier will quote on their invoice. |
| Buyer and supplier details | Legal names, addresses and contact people on both sides. |
| Order date | When the purchase was authorised. |
| Items or services | Description, quantity, unit price and any product codes, specific enough to avoid ambiguity. |
| Total and currency | The agreed amount, and whether tax is included or added. |
| Delivery details | Address, required date and any shipping terms. |
| Payment terms | For example Net 30, or a deposit and balance. |
| Approval | Who authorised the purchase, if your process requires sign-off. |
Tax treatment differs between countries. Some buyers state prices excluding sales tax, VAT or GST and let the supplier's invoice add it; others agree a tax-inclusive price. Whichever you choose, say so on the PO.
Purchase order vs quote vs invoice
The three documents are easy to confuse because they often describe the same items and the same total. What differs is who sends them, when, and what they commit each side to.
| Quote | Purchase order | Invoice | |
|---|---|---|---|
| Sent by | Seller | Buyer | Seller |
| When | Before the buyer decides | After the buyer approves | After delivery |
| Purpose | Offer a price | Authorise and confirm the purchase | Request payment |
| Creates a payment obligation? | No | Not on its own | Yes, once goods or services are supplied |
| Recorded in accounts as | Nothing yet | A commitment (by some buyers) | A payable (buyer) and receivable (seller) |
How does the purchase order process work?
- Need identified. Someone needs goods or a service. In larger organisations this starts as an internal purchase requisition.
- Quote obtained. The supplier provides a price and terms.
- PO issued. The buyer approves the spend and sends a numbered purchase order.
- Supplier accepts. The supplier confirms, sometimes with a formal order acknowledgement.
- Delivery. Goods arrive with a delivery note, or the service is completed. The buyer records what was actually received.
- Invoice. The supplier invoices, quoting the PO number.
- Match and pay. The buyer checks the invoice against the PO and the delivery, then pays on the agreed terms.
For the difference between the documents at the end of that chain, see invoice vs receipt.
What is three-way matching?
Three-way matching is the check a buyer runs before paying: does the invoice agree with the purchase order, and do both agree with what was actually delivered? It catches overbilling, short deliveries and duplicate invoices before money leaves the account.
A simple example. A café group issues PO-1042 for 200 cases of cups at $12.50, a total of $2,500. Only 180 cases arrive. The supplier's invoice should be for $2,250, not $2,500. Because the PO, the delivery record and the invoice all have to agree, the $250 difference is spotted before payment rather than argued about afterwards.
What types of purchase order are there?
| Type | What it is | Typical use |
|---|---|---|
| Standard PO | A one-off order with fixed items, quantities, price and date. | Most everyday purchases. |
| Planned PO | Items and prices are fixed, but delivery dates are released later. | Known needs with uncertain timing. |
| Blanket PO | An agreement to buy over a period, often up to a spending limit, with individual releases against it. | Recurring supplies such as packaging or stationery. |
| Contract PO | Sets agreed terms with a supplier; separate orders are placed against it. | Ongoing supplier relationships. |
Terminology varies between organisations and software systems, but the ideas are consistent.
What should you do when a client sends you a PO?
If you sell to larger businesses, you'll often be on the receiving end of purchase orders.
- Check it against your quote before starting work. If the price, quantity or terms differ, raise it now.
- Read the terms attached. Some POs carry the buyer's standard conditions, which may differ from yours on payment timing or liability.
- Put the PO number on your invoice. An invoice missing it is one of the most common reasons large clients pay late. The invoice fields checklist covers where it goes.
- Don't exceed the PO value. If the work grows, ask for an amended PO first. Invoices above the approved amount often stall in approval.
What are common purchase order mistakes?
- Vague descriptions. "Marketing services" or "office supplies" invites disputes. Name the deliverable, quantity and unit price.
- Raising the PO after the invoice. A PO created to match an invoice that has already arrived provides no control. It should come before the commitment.
- Silent changes. Quantities or prices changed by phone or email, without an amended PO, leave the invoice and the PO disagreeing.
- Not closing completed POs. Open POs for work that has finished overstate committed spending and can allow a second invoice to be matched against them.
- Ignoring tax and currency. For cross-border purchases especially, state the currency and whether prices include sales tax, VAT or GST.
When does a small business need purchase orders?
A formal PO system is overhead, so it's worth adding only when the benefit is real. Signals that it's time:
- More than one person can commit the business to spending.
- You regularly dispute invoices with suppliers over what was agreed.
- Purchases are large enough that a mistake would hurt.
- You want to see committed spending before the invoices arrive.
A shared spreadsheet with a PO number, supplier, amount, approver and status is enough to start. Accounting and procurement software can take over once volume justifies it.
A simple way to keep the process light is an approval threshold. For example: purchases under a set amount can be made by anyone with a budget; above it, a PO must be approved by the owner or a manager before the order is placed. Pick a threshold that catches the purchases that matter without slowing down everyday supplies, and review it as the business grows.