Works order, sales order, purchase order: which document does what
A works order instructs your own team to do a job. A sales order records what the customer bought. A purchase order commits you to a supplier. All three can appear on the same job - and businesses that run them off one document lose the ability to say what a job actually cost.
A works order tells your own team or your own workshop to do something. A sales order is the record of what a customer agreed to buy. A purchase order commits your business to paying a supplier for goods or services. All three documents can appear on the same job, and all three record different things. The businesses that run into trouble are the ones using one document to do all three jobs, because once that happens, the question "what did that job actually cost us?" no longer has a reliable answer.
What a Works Order Actually Controls
A works order is an internal authorization. It describes a task - a production run, a repair, a custom build, a field installation - and assigns it to specific people or a specific workshop. It carries the details of what is to be done: the materials to be drawn from stock, the labor required, the timeline, and the reference back to the customer order that triggered it.
The key point is that a works order is internal. It does not buy anything from a supplier, and it is not sent to a customer. It moves authorization and specification inside your business, from whoever manages the job to whoever executes it. In a promotional merchandise business, a works order might cover a production run for 500 branded bags. In a joinery workshop, it authorizes a piece of furniture to be built to a specific customer specification. In a renewables installation business, it instructs a field crew to carry out an installation at a named site. In every case, the works order gives the people doing the work the authority and the detail to proceed.
Works order vs job sheet
A works order is a formal internal authorization with a defined scope, materials list, and status. A job sheet is often a simpler field form used to record what actually happened. Both are useful; they do different things.
Where the Sales Order Fits
A sales order records what the customer agreed to buy - the products, quantities, prices, and delivery terms. It is created after the customer accepts a quote or places an order. From that point, it serves as the internal record of the commercial commitment: what was sold, at what price, and when it needs to be delivered.
The sales order and the works order often follow each other on the same job. The sales order captures what the customer ordered; the works order instructs the team that has to build or fulfill it. They are related documents, but they answer different questions. The sales order answers "what did the customer pay for?" The works order answers "what does the team need to do?"
Conflating the two is a common source of margin problems. If a works order is being used as the primary job reference by the production team, but it was built from a quote that the customer never formally confirmed, the team may be building to a specification or price that has since changed. The two documents need to exist separately so that both remain accurate - and so that any post-sale changes are tracked against the right record.
A sales order is money coming in, a purchase order is money going out, and a works order is the work in between.
The Purchase Order Completes the Cost Picture
A purchase order commits your business to paying a supplier. It goes outward - to a vendor - for raw materials, components, sub-contracted services, or bought-in goods. Once a supplier accepts a purchase order, your business is committed to the price and the terms stated on it.
On most jobs of any size, purchase orders and works orders run in parallel. A works order authorizes the internal labor. The purchase orders buy the materials or external services needed to complete that job. A fit-out contractor running a partitioning job will have a works order for the installation crew and purchase orders out to the systems supplier and fixings distributor. A promotional merchandise business running a decorated clothing order will have a works order for the decoration process and purchase orders to blank goods suppliers and any sub-contracted decorator.
The total cost of the job is only visible when you combine both sides: the labor and internal material costs captured in the works order, plus the committed external spend across all associated purchase orders. Neither document alone gives the full picture.
Three-document job costing
A complete cost record for any job needs three inputs - the sales order showing what price was agreed, the works order recording internal labor and materials, and the purchase orders capturing what was spent externally. Remove any one of these and you are estimating, not measuring.
Why One Document Cannot Do All Three Jobs
Some businesses handle all three functions - customer commitment, internal instruction, and supplier commitment - through email or a single generic order form. The short-term convenience is clear. The long-term problem is that you can no longer separate what you sold from what you did from what you spent.
If a single job sheet doubles as the works instruction and also captures supplier costs in the same notes field, then asking "what did this job cost in labor versus bought-in materials?" becomes a manual exercise through email threads and estimates. If the sales order doubles as the production instruction, any change a customer requests after placing the order may or may not reach the people doing the work.
The works orders feature in Zigaflow is built around that separation. A job record captures the customer-facing commitment; a separate works order carries the internal production instruction, linked back to the job so that costs and status flow together without collapsing into the same document. Supplier costs come in through purchase orders linked to the same job, so the final cost picture is assembled from three distinct records rather than pieced together from one.
The case for keeping those three documents separate is not about paperwork discipline. It is that when a job is complete and the invoice is raised, the question of profitability should not require reconstruction from memory. It should be a matter of reading three linked records: the sales order that set the price, the works order that recorded what the team did, and the purchase orders that show what you spent externally. Businesses that merged those records into one cannot answer that question cleanly - and in project-based work, the ones that cannot answer it are also the ones most likely to reprice the next job wrong.
Sources
- Purchase Order vs Work Order: What Is the Difference?PurchaseOrders.io · accessed 2026-09-18
- Sales Orders vs Work Orders - What's The Difference?Celerant Technology · accessed 2026-09-18
- Sales Order vs Purchase Order: DifferencesSpendflo · accessed 2026-09-18