Model Railroad Track Calculator

The calculator takes the larger of your scale's built-in minimum radius and whatever value you enter, so it will never recommend a radius tighter than what that scale's trains can reliably run on — HO scale, for example, always uses at least 18" even if you type in 12". Entering a radius larger than the minimum does work as expected, since a wider curve is always achievable if your minimum allows it.

It takes the larger of your table's width and length, then subtracts two curve radii — one for the train to run into a curve, one to run out — to estimate the longest straight run available for a train or siding. This is a simplified planning number based on your benchwork's overall footprint, not a routed track plan, so your actual usable straight length depends heavily on where curves and turnouts actually sit on the layout.

It's calculated as 60% of your recommended minimum radius, a rough stand-in for how much benchwork space a standard commercial turnout occupies. Real turnout lengths vary by manufacturer and turnout number (a #4 is shorter than a #8, for instance), so treat this as a planning estimate to reserve space, not a substitute for checking the actual dimensions of the turnout you intend to buy.

Each scale in the calculator carries its own built-in maximum grade — N and O scale at 3%, HO at 4%, and G at 2.5% — reflecting typical hobby practice for how steep a grade that scale's locomotives can climb while still pulling a reasonable train length without wheel slip. These are fixed lookup values tied to your scale selection, not derived from your table dimensions or curve radius.