Purchase Order (PO)

Definition

A purchase order, or PO, is a numbered document that a buyer sends to a supplier to order specific goods or services at stated prices and terms. It lists what the buyer wants, how many, what each one costs, where and when it should arrive, and when it will be paid.

The easiest way to picture it is a written order slip. The buyer writes down exactly what they want, the supplier agrees, and from then on every delivery and every bill gets checked against that slip.

One detail trips people up. Many websites call a PO a legally binding contract the moment it is sent, and that is only half right. A PO is usually the buyer’s offer. A contract forms when the supplier accepts it, either by confirming in writing or by shipping the goods (U.S. sales law, UCC § 2-206).

What it contains

A PO holds everything the supplier needs to fill the order and everything the buyer needs to check it later. It has five main parts.

The identifiers

Every PO carries a unique PO number and an issue date, plus a revision number if the PO has been changed. The supplier is expected to quote the PO number on its invoice, which is how the buyer’s team links the bill back to the order.

The parties

The PO names the buyer and the supplier and gives their addresses. It also has a ship-to address, which is where the goods go, and a bill-to address, which is where the invoice goes.

The line items

Each product or service gets its own row. A row shows the item or SKU (the supplier’s stock code), the quantity, the unit of measure, the unit price, and the line total.

The terms

The PO states the date the goods are needed, the payment terms (Net 30 means pay within 30 days), the shipping terms, and the buyer’s terms and conditions.

The approval

A signature or electronic approval shows that someone with spending authority said yes.

Where it’s used

Any business that buys on credit uses POs, and they are especially common in manufacturing, logistics, warehousing, distribution, construction, healthcare, and government. Inside a buying company, five roles usually touch a PO.

The requester

The requester is the person who needs something, such as a production planner, maintenance supervisor, or warehouse manager. They start the process by asking to buy it.

The approver

The approver is a budget holder, plant manager, or finance lead who decides whether the company will spend the money. Larger orders often need a higher level of approval.

Procurement

The procurement team picks the supplier, issues the PO, and chases the supplier for confirmations and changes.

Receiving and quality

Warehouse staff check what arrives against the PO and record a goods receipt note, or GRN, which is a record of what was delivered. Inspectors record how much passed their checks.

Accounts payable

The accounts payable team, called AP, matches each invoice to the PO and pays it.

On the supplier’s side, sales and order processing receive the PO and turn it into a sales order, which is the supplier’s own internal record of the same deal. Billing then sends an invoice with your PO number on it.

A PO shows up early in the buying process. The full path from need to payment is called procure-to-pay, and the PO sits between the approved purchase request and the supplier’s invoice. Everything after it gets checked against it.

How it’s used

The process runs in a fixed order.

Request and approve

The process starts with a purchase requisition, which is an internal request for permission to buy something. A requisition creates no promise to any supplier. A budget holder reviews it and approves or rejects it based on spending limits.

Create and send the PO

Once a request is approved, procurement turns it into a PO. The buyer adds the supplier, price, terms, and accounting codes, then sends it by email, a supplier portal, EDI (a standard format for computer-to-computer orders), or print.

Supplier acknowledges

The supplier replies to confirm the order, usually with a delivery date, or simply ships the goods. If the reply has different terms than the PO, U.S. sales law (UCC § 2-207) still usually treats it as a deal, but the supplier’s extra terms only count in limited cases. A PO can protect itself by saying that acceptance is limited to its own terms. This is general information, not legal advice.

Receive the goods

When the delivery arrives, the receiver checks it against the PO for the right item, quantity, and condition, then records a GRN. If the order needs a quality check, an inspector also records how many units were accepted.

Match the invoice

The supplier’s invoice arrives with the PO number on it. Before paying, AP compares the invoice with the PO and the delivery records. There are three levels of this check, called matching.

2-way match

A 2-way match compares the PO and the invoice. It is often used for services, where there is no delivery to count.

3-way match

A 3-way match adds the goods receipt. The quantity billed should not be higher than the quantity received, which makes it a common check for physical goods.

4-way match

A 4-way match adds the inspection result. The quantity billed should not be higher than the quantity accepted, so it fits goods that need quality checks, such as manufacturing parts.

Systems allow small differences within a set tolerance, which is the size of the gap the company will accept. Outside that tolerance, the invoice goes on hold.

Pay or fix the mismatch

If everything matches, the invoice is paid under the PO’s payment terms and the PO is closed. If something does not match, the fix depends on the gap. For a quantity gap, the buyer waits for the rest of the delivery, corrects the receipt, or asks the supplier for a corrected invoice or a credit note, which is a document that reduces what is owed. For a price gap, the buyer either amends the PO, if the PO price was wrong, or asks the supplier to credit the difference.

Change the PO after it is sent

Sometimes a PO has to change after it goes out. The change should be recorded as a numbered revision, usually with a new approval, and with a new acknowledgment from the supplier when the buyer requires one.

In practice, the hardest part is not the process itself. It is lining up documents that live in different places, such as a PO in the ERP, a goods receipt in a warehouse tool, and an invoice in someone’s email inbox. Even strong finance teams slip.

A 2020 benchmark from APQC found that even top-performing companies say about 0.8% of their yearly payments are duplicates or errors.

Example

An AP specialist at a metal fabrication plant opens her queue on Monday morning. The plant ordered 20 tons of cold-rolled steel coil on a standard PO with Net 45 terms. Last week, the warehouse received 19.6 tons and recorded the delivery. This morning, the mill’s invoice arrived for the full 20 tons.

She runs a 3-way match. The PO says 20, the receipt says 19.6, and the invoice says 20. The billed quantity is higher than what arrived, and the gap is outside the plant’s tolerance, so the invoice goes on hold. She emails the mill, which sends a corrected invoice for 19.6 tons. This time it matches, and it goes into the payment run.

Now change one detail. If the plant were buying machined brackets that need an incoming quality check, it would match 4-way. Say 5,000 brackets arrive and an inspector accepts 4,850. An invoice for 5,000 would be held until the 150 rejected brackets were returned and credited, even though the delivery record says 5,000.

Visual anatomy

Where each key field sits on a typical purchase order.

Types

Companies use four main types of PO, depending on how much they know when they place the order.

Standard purchase order

A standard purchase order is a one-time order where the buyer already knows the item, price, quantity, delivery date, and accounting. It is the simplest type and fits any purchase that happens once. Procurement issues it, and AP matches it against one delivery and one invoice. A plant ordering steel coil for next month’s production run would typically use this type.

Planned purchase order

A planned purchase order is a promise to buy set quantities from one supplier over time, with delivery dates that are only tentative. The buyer places the actual orders later, as scheduled releases against the planned PO, once the timing firms up. It fits supply that follows a forecast, and procurement manages the releases as demand becomes clear. A manufacturer that knows it needs a fixed quantity of a component over the year, and sets each shipment as production plans become firm, would use this type.

Blanket purchase order

A blanket purchase order is an agreement for items the buyer purchases again and again from one supplier. The prices are often agreed up front, but the quantities and delivery dates are left open. Each actual order is a release against the blanket, and the type is also called a standing order. It suits everyday supplies like packaging, consumables, and maintenance parts. A warehouse that agrees on box prices with a supplier for 12 months, then sends a release each week for what it needs, is using this type.

Contract purchase order

A contract purchase order sets the terms with a supplier, such as payment, liability, delivery, and quality, without naming any specific items or quantities. Later POs refer back to it, so each new order starts with the terms already agreed. It fits suppliers the buyer expects to use for many different orders, such as carriers, contract manufacturers, and service vendors. For example, a trucking company might sign one with a subcontract carrier, then send individual load orders that refer back to it.

Note: many websites blur blanket and planned POs. The simple difference is that a planned PO fixes the quantities up front, while a blanket PO leaves them open. Purchasing software may also use other names for these, such as “purchase agreement” or “framework agreement,” but the ideas are the same.

A release order is not a fifth type. It is the actual order placed under a blanket, planned, or contract agreement.

Variations

Purchase order vs. Purchase requisition

A purchase requisition is an internal request for permission to buy, and it creates no promise to anyone outside the company. A purchase order is what goes to the supplier once that request is approved. Small companies sometimes skip the requisition and issue POs directly. The requester usually writes the requisition, and procurement writes the PO.

Purchase order vs. Order acknowledgment

The PO is the buyer’s offer, and the order acknowledgment is the supplier’s reply. The reply confirms the order and often adds a delivery date and quantity. In the U.S., the acknowledgment is usually the acceptance, and if its terms differ from the PO, UCC § 2-207 decides which terms count.

Purchase order vs. Sales order

These two documents describe the same deal from opposite sides. The PO belongs to the buyer. The sales order is the supplier’s own internal copy, which order processing creates from your PO to drive shipping and billing. A good sales order carries your PO number, so the final invoice can be matched back to your order.

Purchase order vs. Invoice

A PO comes before delivery. It says what is being ordered and sets aside budget. An invoice comes after delivery and asks for payment. AP compares the two, and usually the goods receipt too, before paying.

FAQs