How many screens should an HMI have?

Fewer than most have. The count follows from the tasks the operator performs, not from the equipment list. A plant with forty motors does not need forty screens; it needs one screen per area the operator controls as a unit, plus detail screens reached from them.

What belongs on the overview screen?

The whole process, at a glance, with no navigation. Key flows, levels, states and any active abnormality. It answers one question: is everything normal? It is not a menu, and putting navigation buttons on it instead of process information is the commonest mistake.

How deep should navigation go?

Any working screen should be reachable in one action from anywhere. Two levels of menu to reach a screen an operator visits hourly is a design that will be worked around with a stack of favourites.

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HMI & SCADA·6 min read·August 20, 2026

How many HMI screens, and what goes on each

Four levels, the navigation that connects them, and the test for whether a screen earns its place.

Short answer

Four levels: a process overview with no navigation needed, unit control screens where the operator works, detail screens for diagnosis, and support screens for trends and documentation. Navigation should reach any level 2 screen in one action from anywhere. A screen earns its place if it answers a question the operator actually asks; screens built per piece of equipment rather than per task are how a plant ends up with fifty nobody uses.

The number of screens on an HMI is usually decided by the equipment list, which is why so many plants have one screen per pump and no screen showing the plant.

Start from the tasks

The right question is not what equipment exists. It is what the operator does.

Start the line. Change over to a different product. Investigate why the fill weight is drifting. Hand over to the next shift. Deal with a trip at three in the morning with nobody else in the building.

Each of those is a task, each needs particular information together, and a screen is the answer to a task.

Level 1: the overview

One screen, the whole process, no navigation required to understand it.

It answers a single question: is anything wrong? An operator glancing at it from the other side of the room should be able to tell.

This screen is skipped more often than any other because it is the hardest to design and the least obviously necessary. It is also the one that turns a set of screens into a control system.

Level 2: unit control

Where the operator spends the shift. One screen per area they control as a unit, with the controls, the key values and the states for that area.

The test for what belongs: could the operator run this area for an hour from this screen alone, without navigating away? If not, something needed is on another screen and should not be.

Level 3: detail

One loop, one machine, one sub-assembly. Reached from level 2 by clicking the thing you want to know about, which is the only navigation that never has to be learned.

Diagnostics, individual device status, manual overrides, the parameters an engineer needs and an operator does not.

Level 4: support

Trends, alarm history, batch records, help, documentation. Everything consulted rather than operated.

Trends deserve saying out loud: they are consulted far more than most designs assume. An operator asking whether a value is drifting cannot answer it from a number, and a plant with no accessible trends has an operator who cannot answer the most common question they have.

Navigation that survives

Three rules cover most of it.

A persistent navigation bar, in the same place on every screen, reaching every level 2 screen.
Click the object to get its detail. Never a separate menu listing the same objects by name.
The alarm banner is on every screen, in the same place, and is never covered by a popup.

The test for a screen

Before adding one, write down the question it answers and who asks it.

If the question is 'what is the state of the recirculation pump', that is a detail view of an object on a level 2 screen, not a screen. If it is 'why is the line running slow', that might genuinely be a screen, because answering it needs several things together that live in different places.

Screens created because a piece of equipment was delivered are the ones nobody opens.

Common questions

How many screens should an HMI have?: Fewer than most have. The count follows from the tasks the operator performs, not from the equipment list. A plant with forty motors does not need forty screens; it needs one screen per area the operator controls as a unit, plus detail screens reached from them.
What belongs on the overview screen?: The whole process, at a glance, with no navigation. Key flows, levels, states and any active abnormality. It answers one question: is everything normal? It is not a menu, and putting navigation buttons on it instead of process information is the commonest mistake.
How deep should navigation go?: Any working screen should be reachable in one action from anywhere. Two levels of menu to reach a screen an operator visits hourly is a design that will be worked around with a stack of favourites.