If you’ve started looking into ways to measure how users feel about your product, you’ve might be familiar with two acronyms: SUS and NPS. They both produce a number. They both involve asking your users questions. They’re both widely used.

But they measure fundamentally different things — and confusing them is one of the most common mistakes product teams make when they start taking user feedback seriously.

Here’s what each one is, what it actually tells you, and how to think about using them together.

What is NPS?

NPS stands for Net Promoter Score. It was developed by Fred Reichheld and introduced in a 2003 Harvard Business Review article, and it has since become one of the most widely used customer metrics in the world.

The survey is a single question:

“On a scale of 0–10, how likely are you to recommend this product to a friend or colleague?”

Respondents are then grouped into three categories based on their answer:

• Promoters (score 9–10) — loyal enthusiasts who will recommend you
• Passives (score 7–8) — satisfied but unenthusiastic
• Detractors (score 0–6) — unhappy users who may actively discourage others

Your NPS is calculated by subtracting the percentage of Detractors from the percentage of Promoters. The result is a number between -100 and +100. A positive score is generally considered good. Above 50 is considered excellent. Above 70 is world-class.

NPS is simple, fast, and easy to benchmark against other companies in your industry. That’s why it caught on so quickly.

What is SUS?

The System Usability Scale (SUS) is a 10-question survey that measures how usable your product feels to the people who use it. It was developed in 1986 by John Brooke — more than fifteen years before NPS existed — and has accumulated over 20,000 academic citations across four decades of use.

Rather than one broad question about loyalty, SUS asks users to agree or disagree with ten specific statements about their experience — things like “I found this system unnecessarily complex” and “I thought the system was easy to use.” Their responses are combined into a score between 0 and 100, with 68 being the industry average.

Unlike NPS, SUS is focused specifically on usability: how easy, learnable, and consistent the product feels to use. Not whether they’d recommend it. Not whether they’re satisfied overall. Whether it works well.

The core difference: loyalty vs. usability

This is the key distinction, and it’s worth being precise about it.

NPS measures loyalty. It tells you how your users feel about your product in an overall, emotional sense. A high NPS means users like you enough to stake their reputation on recommending you. A low NPS means something is wrong — but it doesn’t tell you what.

SUS measures usability. It tells you how easy your product is to use. A high SUS means users can accomplish what they’re trying to do without friction. A low SUS points specifically to the experience of using the product — not to pricing, support, or any other factor.

Think of it this way. A user might give you a 9 on NPS — they love what your product does for them and would happily recommend it — while still finding it genuinely difficult to use. They’re loyal despite the friction, not because the experience is great.

Equally, a product could have excellent usability (high SUS) but still have low NPS because users are unhappy about pricing, customer support, or how a competitor compares.

Neither number tells the whole story. Together, they tell you a great deal.

A practical example

Imagine you run a project management tool. You send an NPS survey and get a score of 32. That’s below average — something is clearly wrong. But what?

It could be the price. It could be a missing feature. It could be that onboarding is confusing. It could be that a competitor just launched something better. NPS can’t tell you.

Now you run a SUS survey. Your score comes back at 54 — below average. That’s a specific signal: users are finding the product hard to use. The friction is in the experience itself, not in how you’re priced or marketed.

That’s actionable. You know where to look. You improve the onboarding flow, simplify the navigation, and run the SUS survey again three months later. The score moves to 69. You run NPS again. It starts to climb.

This is the pattern: SUS tells you whether the product is getting easier to use. NPS tells you whether that improvement is translating into loyalty and advocacy.

Which one should you track?

Both — but if you’re starting from scratch, start with SUS.

NPS is a lagging indicator. It reflects how users feel about you after a long period of experience, including factors well outside your product team’s direct control. It’s useful for tracking overall business health, but it’s slow to move and hard to act on directly.

SUS is a leading indicator of the things NPS cares about. Usability drives satisfaction. Satisfaction drives loyalty. Loyalty drives recommendation. If your SUS score is low, your NPS is likely to follow — often with a lag of several months.

By tracking SUS consistently across releases, you can see the effect of your product decisions quickly, before they show up in NPS. You get a faster feedback loop. You can course-correct earlier.

Once you have a SUS baseline established, adding NPS gives you the broader picture — and the two numbers together start to tell a coherent story about where your product stands and where it’s heading.

A note on survey fatigue

One practical consideration: both surveys ask something of your users. Don’t run them simultaneously, and don’t run either one so frequently that users start ignoring them.

A reasonable cadence for SUS is after major releases or on a quarterly schedule. NPS is typically sent every six months, or triggered by specific moments in the user journey (after 30 days of use, for example).

Keep them separate. Each measures something distinct, and mixing them muddies both signals.

The bottom line

NPS tells you whether users love you. SUS tells you whether your product is easy to use. Both matter. Neither replaces the other.

If you’re only tracking one thing right now, track SUS. It’s more directly connected to product decisions, faster to respond to changes, and gives your team something concrete to improve against.

Then, once you have a usability baseline, layer NPS in to understand whether the work you’re doing is translating into the loyalty and advocacy that drives growth.