- The PO number does two jobs, and most people only use one
- Purchase order vs invoice vs sales order
- How a purchase order moves from request to payment
- What to put on a purchase order
- The five types of purchase order
- What a PO protects you from
- Where I come in
- My verdict on purchase orders
- Frequently asked questions
A purchase order (PO) is the document a buyer sends to a supplier to order goods or services, setting out what's being bought, how many and at what price. Once the seller accepts it, Corporate Finance Institute (CFI) says it becomes a legally binding contract for both sides.
CFI describes it as a commercial source document issued by a business's purchasing department when it places an order with a vendor. Its plainest line is the one worth remembering: a PO is the contract drafted by the buyer when buying from the seller.
HubSpot adds the practical detail. A purchase order states what's being ordered, the price, the date of the order and contact details for both parties. It may also carry payment terms and taxes, and every one has its own unique PO number. That number turns out to be the most useful thing on the page.
The PO number does two jobs, and most people only use one
CFI says the PO number has two jobs. First, it makes sure the goods you ordered match the goods you received. Second, it's matched to the supplier's invoice, so you're charged the right amount. Lose the number, or let a supplier invoice without it, and both checks fall away.
HubSpot describes the same step from the accounts side. The accounts payable team matches the invoice against the PO to make sure what was delivered is what was ordered. If the PO number, the invoice and the work delivered all line up, the invoice goes on for approval. If they don't, it stops there, which is the whole point.
There's one more term you'll hear. CFI calls a PO 'open' when the order's been placed but the goods haven't all arrived yet. It stays open until everything's in.
Purchase order vs invoice vs sales order
These three get mixed up all the time, mostly because they describe the same deal from different sides. CFI is clear about who sends what.
| Document | Who sends it | What it does |
|---|---|---|
| Purchase requisition | Internal request to purchasing | Asks for approval to buy (CFI) |
| Purchase order | Buyer | Orders the goods; binding once the seller accepts it (CFI) |
| Sales order | Seller | Confirms or approves the sale (CFI) |
| Invoice | Seller | Says what the buyer must pay; matched to the PO number |
CFI sums up the difference in one sentence: the PO is a contract of sale, while the invoice is the confirmation of the sale. So the PO comes first and comes from the buyer. The invoice comes later and comes from the seller.
How a purchase order moves from request to payment
CFI sets out the ordering process in four steps, and HubSpot's matching step completes it. Put together, it runs like this.
- The buyer raises a purchase requisition, an internal document that tracks what's being ordered, and an authorised manager approves it.
- The buyer issues the PO. CFI lists what goes on it: the date, FOB shipping information, discount terms, the buyer's and seller's names, a description of the goods, the item number, price, quantity and the PO number.
- The seller accepts or rejects it. Acceptance is what makes it binding on both of you.
- The buyer records the PO, and it stays open until all the goods arrive.
- The invoice arrives and is matched to the PO number before anyone pays it.
What to put on a purchase order
HubSpot's list of what a PO should include is short, and that's a good thing. You don't need a complicated form.
- The PO number, unique to this order.
- The names of both businesses, with physical addresses and contact details.
- The items ordered and their prices.
- Any discounts, tax information and shipping costs.
- The payment terms.
A printing business HubSpot spoke to uses a simple internal template: PO number, buyer and vendor details, item descriptions, quantities, agreed prices, terms and delivery instructions. HubSpot says a spreadsheet works, but it recommends tying your POs into your accounting software. If you're at that point, my roundup of purchase order software compares the tools that do it.
The five types of purchase order
Not every order is a one-off. HubSpot lists five kinds, and picking the right one saves a lot of paperwork if you buy from the same supplier again and again.
Want AI doing the heavy lifting in your marketing?
I build the systems that handle the boring 80 percent, so you get your week back. Done properly, with the human kept in.
| Type | What it's for (HubSpot) |
|---|---|
| Standard | One-off purchases from a company you rarely deal with |
| Blanket | A standing order: a long-term contract that sets prices over a period, with several shipments sharing one PO number |
| Planned | You agree what and how much, then schedule deliveries as needed, such as 1,000 boxes a year sent in batches |
| Contract | Sets pricing and terms for all of a vendor's POs over a time frame; suited to manufacturers and construction |
| Digital | Software that generates, sends and tracks POs |
What a PO protects you from
CFI lists three benefits for the buyer. A PO stops duplicate orders. It keeps track of what's coming in, and a well-organised PO system makes inventory and shipping simpler. And it's a legal document, which helps you avoid disputes. For the supplier, the PO tells them what to take from inventory and what to charge under the payment terms you agreed.
HubSpot quotes a business owner who calls her POs her financial protection. Once the supplier accepts, both sides are legally responsible for those terms, and it lets her see her spending commitments before a single payment goes out. HubSpot adds that a good PO system helps prevent overspending and gives more accurate tracking of stock. If suppliers are a big part of how you run, my tips on managing a small business supply chain pick up where this leaves off.
Where I come in
Buying is a bigger part of growth than most owners think. Tools, freelancers, agencies, events and print all arrive as orders and invoices, and when nobody's matching them, spend drifts. I work with small businesses and SaaS marketing teams on the marketing side of growth, and part of that is helping them see what they're committing to before the bills land. You can see how I work on my work with me page.
My verdict on purchase orders
A PO is cheap protection. It takes a few minutes to raise, and it gives you a binding record of what you agreed and a number to check every invoice against. If you buy from the same suppliers more than once, use them. Put the PO number on every order, ask suppliers to quote it on every invoice, and don't pay anything that doesn't match. That one habit catches mistakes that would otherwise only surface months later.
Frequently asked questions
What is a purchase order in simple terms?
It's the document a buyer sends a supplier to order goods or services, listing items, quantities and prices. CFI says it becomes a legally binding contract once the seller accepts it.
Who issues a purchase order, the buyer or the seller?
The buyer. CFI says the PO is generated by the buyer to order goods, while the invoice is generated by the supplier.
What's the difference between a purchase order and an invoice?
CFI puts it this way: the PO is a contract of sale, while the invoice is the confirmation of the sale. The invoice is matched to the PO number before payment.
What does an open purchase order mean?
It means the order's been placed but the goods haven't all arrived yet. CFI says the PO stays open until everything's received.
Can I use a spreadsheet for purchase orders?
Yes. HubSpot says a spreadsheet works, though it recommends linking your POs to your accounting software as you grow.
