An SOP is internal and prescriptive: it states how your organisation performs a process, and following it is expected. A user guide is usually external and explanatory: it describes what a product does and how to operate it, leaving the reader to decide what they want to achieve.
The clearest way to see the difference is obligation. An SOP can be audited against, because there is a right way. A user guide cannot, because there is no wrong way to use a feature.
Practical differences
- Reader. Your colleagues versus your customers.
- Scope. One process end to end, including handoffs between people, versus one product's capabilities.
- Roles. SOPs name who does each step. User guides address a single undifferentiated "you".
- Decisions. SOPs prescribe which branch to take. User guides describe the options and let the reader choose.
- Approval. SOPs typically need review before they go live. Documentation usually ships with the product.
Where the confusion causes real problems
Teams frequently write a user guide and call it an SOP, most often when the process runs inside one tool. It reads like "here is how the CRM works" rather than "here is how we qualify a lead, who does it, and what happens when it fails qualification". The result documents the software rather than the process, and the moment the work involves a second person or a judgement call, the document has nothing to say.
You may need both
A software vendor needs user guides for customers and SOPs for its own operations. They are not competing documents, and material rarely transfers usefully between them: a screenshot walkthrough of a feature is not a procedure, and a procedure is not helpful to someone evaluating a product.