Finance

What is a purchase order in construction?

A purchase order (PO) is a written commitment from a contractor to a supplier to buy specific materials, equipment, or services at an agreed price, quantity, and delivery date, charged to a specific job and cost code.

Two construction professionals review paper plans beside a tablet at a jobsite workbench.
Plan reviews connect field conditions, drawings, and the next decisions on a job. AI-generated illustration.

A purchase order is how a contractor buys things on purpose. It lists what is being bought, how much, at what price, where and when it should be delivered, and which job and cost code pays for it. When the supplier accepts it, the PO is a contract. Subcontracts cover labor and installed work by another company; POs typically cover materials and equipment that the contractor or a sub installs.

The accounting benefit is just as important. Once a PO is issued, its value becomes a committed cost on the job, even though no invoice has arrived. That lets the PM see the real cost picture weeks before the bills show up.

How a PO works on a real job

Say a GC on a three-story office building needs hollow metal doors and frames. The budget line is $58,000. The project manager gets three quotes, picks a supplier at $54,750, and issues this PO.

Example purchase order summary
FieldEntry
PO number2417-031
Job / cost code2417 Office Building / 08 doors and frames
Items42 frames, 38 doors, per approved submittal
Price$54,750 lump sum, freight included
DeliveryFloors 1 and 2 by week 14, floor 3 by week 17
TermsNet 30, partial deliveries billed separately
ReferencesHardware schedule rev 2, shop drawings approved

When the first shipment arrives, the super checks the packing slip against the PO. When the supplier's invoice comes in, accounts payable runs a three-way match: PO, receiving record, and invoice. If the invoice shows $56,900 because of a fuel surcharge the PO did not allow, AP flags it before it gets paid.

Why POs matter for margin

  • Locks in price. Quotes expire. A PO accepted by the supplier holds the number.
  • Shows committed cost early. Job cost reports without POs look better than reality until invoices land.
  • Stops duplicate and unauthorized buying. Two foremen ordering the same lumber is a real and common leak.
  • Ties delivery to the schedule. Lead times and delivery windows are written down, which helps with long-lead items.
  • Supports change order pricing. Clean PO records prove what material actually cost.

Common PO mistakes

  1. Issuing the PO after the material shows up, which defeats the point.
  2. Leaving out the submittal revision, so the supplier ships the old spec.
  3. Not using blanket purchase orders for repeat consumables, which buries the office in tiny POs.
  4. Skipping the receiving step, so short shipments get paid in full.
  5. Not updating the PO when quantities change, so committed cost is wrong.

On smaller jobs the PO can be a one-page form or a line in a log, as long as it captures vendor, job, cost code, quantity, price, and delivery date before the order is placed. What matters is that the commitment exists in writing before the money is spent, so the project manager and the bookkeeper are looking at the same number when the invoice arrives.

Related terms

POs are part of procurement and buyout, feed job costing, and flow into accounts payable. For process detail, see how to manage construction purchase orders. Smart Business Automator records POs as commitments against each job's budget and tracks the shipments tied to them.

Frequently asked questions

Is a purchase order legally binding?

Once the supplier accepts it, by signing or by shipping, a PO generally works as a contract for the goods. Its terms and the supplier's own terms can conflict, so read both on big orders.

What is the difference between a PO and a subcontract?

A PO usually buys materials or equipment. A subcontract hires another company to perform part of the work, often including labor and installation, and carries more contract terms.

Do small contractors need purchase orders?

Not for every $40 box of screws, but for anything significant, yes. Even a simple PO log with job, vendor, amount, and date improves job cost accuracy.

What is a three-way match?

Comparing the PO, the receiving record or packing slip, and the vendor invoice before paying. All three should agree on item, quantity, and price.

Written and edited by

Maurice Francois writes and edits construction operations guides for Smart Business Automator. More from Maurice on the Scaling Legends podcast.

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