How to write a purchase order
A purchase order is the buyer’s document. It says what you will buy, at what unit price, and where it should go. The invoice comes later, from the seller. If the PO is vague, accounts payable ends up negotiating a bill that nobody agreed to.
This is a working guide for a small office in the United States, the United Kingdom, or Canada. It is not a substitute for your accountant, and it is not a tax opinion. The form that matches these fields is the Halden purchase order generator.
When a small office actually needs one
You do not need a purchase order for every coffee run. You need one when the amount is above a threshold you wrote down, when more than one person can say “I ordered that,” or when the vendor will not ship without a number. Many offices of about ten people set the line at 250 or 500 in their currency. Put the number in a sentence your staff can find. Halden will not enforce it. A tool that pretends to be your policy is how policies get ignored.
Use a PO for custom work, for anything you might return, and for any supplier who has billed you for a quantity you did not get. Skip a fresh PO for the electric bill, the lease, and a software subscription that already has a contract. Those commitments live in the contract. A second document with a new number does not make them clearer.
The fields that have to be true
Start with identity. The buyer block is your legal or trading name, the email that should receive the acknowledgement, a phone number a dispatcher will actually answer, and the address you want on their file. The vendor block is their name as it appears on their bill, not the nickname on the packing tape. If they gave you an account number, put it on the order. It is the fastest way their clerk finds you.
Then the control fields. A unique PO number. An issue date. A needed-by date that a human could meet. A ship-to that is a door, not “the office.” Payment terms in words a stranger can apply: Net 30 means thirty days from their invoice date, not thirty days from the afternoon you felt like paying. “As discussed” is not a price and it is not a term.
Each line needs a description a receiver can check, a quantity, a unit, and a unit price. SKU helps when the vendor has one. A line that says only “supplies” cannot be received, cannot be matched, and cannot be disputed. Freight is either its own line or the shipping box on the total, and the notes should say who arranged it. Tax is a rate, not a hope. Halden will multiply the rate you type. It will not look up sales tax, VAT, or GST, because those lookups are wrong often enough to be expensive.
A worked example
Northwater Studio, a twelve-person office, orders from Brightline Paper Co.
6 cases of letter paper at 42.50 = 255.00. 2 black toner cartridges at 89.00 = 178.00. 1 dock delivery at 35.00 = 35.00. Subtotal 468.00. No discount. They type a tax rate only if Brightline’s quote includes one. Shipping is already a line, so the shipping box stays at zero and is not taxed twice.
The notes say: deliver weekdays before 2 p.m., partial cases are acceptable, and the invoice must quote the PO number. That last sentence is what makes the later match possible.
You can load those exact lines with “Fill an example” on the generator, then replace the studio’s name with yours. The arithmetic is ordinary. The discipline is putting the unit price on the page before anyone ships.
Number so you can find it in March
Do not use the date alone. Two orders on the same morning will share it. Do not restart at 1 every Monday. A prefix, the year, and a padded sequence is enough: PO-2026-014. A department prefix such as OPS-2026-014 is fine if it stays short enough for an email subject and a packing slip.
Never reuse a cancelled number. Mark the order cancelled and let the counter move. Reuse is how a new bill attaches itself to an old commitment, and how a three-way match fails for a reason nobody remembers. The number generator advances only when you file an order that is using the next number. A hand-typed exception does not burn the sequence.
Send it, then stop editing it in your head
Print to PDF from the browser and email that file. Put the PO number in the subject. If the vendor acknowledges a different price, that acknowledgement is a counteroffer. Amend the order or refuse it. Do not “sort it out on the invoice.” The invoice is their document. If you let it rewrite the deal, you have no deal, only a bill.
File the order before the box arrives. When the goods show up, write what came, the same day. When the bill shows up, match the three. The method, with numbers, is in three-way match. The difference between this document and the bill is in purchase order vs invoice.
Mistakes that get an order bounced
A total with no unit price. A description of “supplies.” A ship-to that is someone’s home when the carrier wanted a commercial dock. Tax assumed instead of stated. Two live orders with one number. A verbal change that never landed on the PDF the vendor has. A needed-by date of tomorrow on a made-to-order item. Any one of these is survivable once. Together they are why a clerk stops reading your emails.
Halden will not stop you from making them. It will keep the fields in front of you, keep the number unique if you let it, and keep the filed copy on this computer so the version you sent is the version you can open next week.