The one thing that confuses people most about modular switches is the sizing — all those “1M”, “2M”, “4M”, “8M” labels. Once it clicks, though, it is genuinely simple, and understanding it is the key to buying the right switches and sockets for your board without ending up short of space or paying for more than you need.

This guide explains what the module sizes mean, how the common components (switches, sockets, regulators) add up, and how to work out how many modules your switchboard actually needs. (If you are still deciding between modular and the older piano switches, start with our modular vs non-modular guide first.)

The basic idea: “M” means one module

In a modular system, “M” is one module unit — the standard building block. Every component is described by how many of these units it occupies:

• A 1M component takes up one module of width.
• A 2M component takes up two.
• A 3M component takes up three, and so on.

These components clip into a frame, and a plate covers the frame to give the finished look. Frames and plates are themselves described by their total capacity — a 2M plate, 4M plate, 6M plate, 8M plate, 12M plate, and so on — meaning how many module-units they can hold in total.

So the whole system is just arithmetic: add up the modules of everything you want on a board, and choose a frame/plate that holds at least that many.

How many modules do common components take?

Here is the part that actually matters when you are planning a board. Module sizes can vary slightly between brands, but as a general guide:

• Switch (6A, one-way/two-way): usually 1M — the basic building block.
• Bell push / indicator: typically 1M.
• 6A socket (small, 3-pin): often 1M.
• 16A socket (larger, for heavy appliances): typically 2M (sometimes 3M depending on brand/type).
• 6A/16A combined socket: commonly 2M–3M.
• Fan regulator (step-type): often 1M; older/rotary types can be larger.
• Blank plate (to fill a gap): 1M (used to keep the plate looking finished where there is a spare slot).

Always check the specific brand’s sizing. These are typical figures, but the exact module count for a given socket or regulator can differ between manufacturers. When buying, confirm the module size printed on the product so your board maths is right.

Working out how many modules you need

The method is straightforward: list everything that goes on the board, add up the modules, then pick the next plate size up.

Worked example — a typical bedroom board might have:

• 2 × light switches (1M each) = 2M
• 1 × fan switch (1M) = 1M
• 1 × fan regulator (1M) = 1M
• 1 × 6A socket (1M) = 1M
• 1 × 16A socket (2M) = 2M

Total = 7M. Since plates come in standard sizes, you would choose an 8M plate — the next size up that fits everything, with a spare 1M slot you can fill with a blank module (or keep for a future addition).

That last point is worth remembering: leaving a spare module or two means you can add a socket or switch later without replacing the whole board. Planning a little headroom is cheap insurance.

Common plate sizes

Modular plates typically come in these capacities (availability varies by brand):

• 1M, 2M, 3M — small boards for one or two components.
• 4M, 6M — common for a cluster of switches, or switches plus a socket.
• 8M, 12M, 16M, 18M — larger boards for busy locations (near a bed, a kitchen counter, a TV unit) with multiple switches, sockets and a regulator.

Bigger plates are simply wider (and sometimes taller, in multiple rows). The right size is whatever holds your module total with a little room to spare.

“Modular sockets and switches” — buying them together

Because switches and sockets share the same module system, you mix them freely on one board — a few switches, a 6A socket, a 16A socket for an appliance, all under one plate. This is the real convenience of the modular system: sockets and switches are part of one coordinated set, in matching finishes, rather than separate mismatched fittings. When you plan a room, think of each board as a little layout of modules and choose the components and plate together.

A quick recap

• “M” = one module unit. Components are 1M, 2M, 3M, etc.
• Plates are sized by total capacity (2M, 4M, 6M, 8M…).
• Add up the modules of everything you want, then pick the next plate size up.
• Leave a spare slot for future additions; fill empty slots with blank modules.
• Check brand-specific sizing — the typical figures above can vary.

Once you are comfortable with sizing, the next decision is which brand to buy — covered in our guide to the best modular switches in India. And if you are weighing modular against the older style, see modular vs non-modular switches.

A quick safety note

Planning a board is something anyone can do, but the actual wiring and installation should be handled by a qualified electrician — especially for 16A circuits serving heavy appliances, which have their own wiring requirements. Switch off at the mains before any work, and if in doubt, call a professional.