What are callipers and why do I need digital one for model railways

Why digital callipers are an essential tool for model railway construction and maintenance.

Whether you’re laying track, fixing rolling stock, or making a model building, accuracy can make all the difference in achieving a realistic and visually stunning layout.

One tool that’s indispensable for achieving this level of precision is the digital calliper.

Here’s why they’re essential for model railway builders,  where they excel over other tools and where they don’t.

What are Callipers?

Callipers are measuring instruments used to accurately determine the distance between two opposite sides of an object.

And there are various types, including:

Vernier Caliper: This is a versatile calliper that uses a sliding scale called a vernier scale to achieve readings, they usually measure the outside, inside and depth.

Inside Caliper: These callipers are designed to measure the diameter or width of holes.

Outside Calipers: As the name suggests, outside callipers are used to measure the external dimensions of objects, such as the thickness of a board or the diameter of a rod.

Divider Caliper aka Spring Calipers: These have two legs connected by a spring and an adjustment mechanism and are used for transferring measurements or marking out distances rather than taking precise measurements themselves.

While I have all of these, it’s vernier callipers that I find myself turning to most often and the digital versions which I’ve found most useful.

Why use digital vernier callipers for model railways?

Digital callipers offer several advantages that make them invaluable in the world of model railways:

  1. Precision: Digital callipers provide highly accurate measurements, typically to within a thousandth of an inch or a hundredth of a millimetre. This level of precision is crucial when working with small-scale models where even the slightest deviation will be very visible and ruin the impression of realism.
  2. Easy-to-read Display: The digital display on these callipers makes readings clear and straightforward, eliminating the potential for misinterpretation that can occur with manual callipers. The large contrast display is also easier on the eyes and saves reaching for the head visor.
  3. Versatility: Digital callipers can measure both inside and outside dimensions, as well as depths, allowing for versatile usage across various aspects of model railway construction.
  4. Zero Function: With the zero function, you can reset the calliper to zero at any point, making it easy to take incremental measurements without the need for manual calculations.
  5. Metric and Imperial Units: Most digital callipers offer the flexibility to switch between metric and imperial units, catering to the preferences of model builders whether their old or new school.

Where callipers are used on model railways

One of the many digital callipers I’ve tested and used when making my models.

Digital callipers find numerous applications in model railway construction:

  1. Track Alignment: Ensuring precise alignment and spacing between tracks is essential for the smooth operation of model trains. Digital callipers can accurately measure the distance between rails, ensuring proper alignment and reducing the risk of derailments.
  2. Rolling Stock Assembly: When assembling locomotives, freight cars, or passenger coaches, precise measurements are crucial for proper fitting of components such as wheels, couplers, and body parts. Digital callipers enable modellers to measure axle distances, wheel diameters, and clearance gaps accurately.
  3. Scratch-building Structures: For modellers constructing model railway buildings and structures, digital callipers aid in achieving accurate dimensions for components such as walls, windows, and doors. My OO gauge braziers for example, are supplied on a base to make them easier to install, and I use the calliphers to measure the internal hole in this base to ensure the LED fits through.
  4. Scenery Detailing: Whether sculpting terrain features or adding foliage and details to scenery, digital callipers can help maintain consistent proportions and dimensions for a realistic landscape.

When not to use digital vernier calipers

While digital callipers excel in many use cases in layout construction and maintenance, there are instances where other dedicated tools may be more appropriate:

  1. Measuring really small parts. For the majority of jobs around a layout, most digital callipers – including my preferred choice – that measure to .001 of a millimeter will be fine. But for really precise measurements to .0001 and beyond a micrometer will be needed. I’ve never needed this resolution on my layouts but if you work on really small scales it’s possible you might need this.
  2. Checking track gauges: When checking the gauge of the track, such as when checking second-hand track, callipers can be used but their length can be a hindrance, particularly if checking track that’s already laid and has scenery or buildings on either side and so prevents you getting the calliper to track level. For this reason, dedicated rolling track gauges are far easier and quicker to use. I love these brass OO/HO gauge ones from DCC Concepts. They’re accurate and can be pulled along the track to easily check the rail widths along sections of the track. They look wonderful too but then I have a thing for old brass tools!
  3. Speciality Measuring Tools: In some cases, specialized measuring tools such as contour gauges or angle finders may be necessary for unique modelling tasks.

My preferred digital vernier callipers

If this has whetted your appetite for digital callipers, and it should, I’ve used these for some time and heartily recommend them. They’re one of my must-have tools for track work and have proven accurate, reliable and robust. (I do have a small brass manual vernier calliper that I use a lot but that’s only because it’s brass and I have a thing about old brass tools).

Notable benefits include stainless steel construction rather than plastic, and a screw holding the battery cover in place – my previous set didn’t have this and the cover fell off never to be seen again 🙁

But regardless of which you choose, get yourself a pair and ensure your trains, tracks and buildings measure up.


Founder of ModelRailwayEngineer, Andy Leaning

Andy is a lifelong modeler, writer, and founder of modelrailwayengineer.com. He has been building model railways, dioramas, and miniatures for over 20 years. His passion for model making and railways began when he was a child, building his first layout at the age of seven.
Andy’s particular passion is making scenery and structures in 4mm scale, which he sells commercially. He is particularly interested in modelling the railways of South West England during the late Victorian/early Edwardian era, although he also enjoys making sci-fi and fantasy figures and dioramas. His website has won several awards, and he is a member of MERG (Model Railway Electronics Group) and the 009 Society.
When not making models, Andy lives in Surrey with his wife and teenage son. Other interests include history, science fiction, photography, and programming. Read more about Andy.

Afflliate disclosure:The links on this page may take you to carefully selected businesses, such as Hornby, Amazon, eBay and Scale Model Scenery, where you can purchase the product under affiliate programmes. This means I receive a small commission on any orders placed although the price you pay does not change. You can read my full affiliate policy here. I also sell my my own ready to use, pre-made and painted buildings and terrain features. browse the range.

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