What is the largest radius OO gauge curve that would fit a 4 ft baseboard?

The average size of a home layout baseboard is 4 ft wide by 6 ft long. If you are planning such a layout, you may well be wondering which radius curves will fit your board.

The good news is, on a 4 ft wide board (that's 1219 mm in new money) you will be able to fit a 4th radius continuous curve onto your layout with 46 mm left to spare (that's 23 mm or just under 1 in. each side of the board). The question is would you want to?

A track located so close to the edge of the board doesn't give any scope for shoulders or scenery so realistic effects will be hard to achieve. You may be better off considering a tighter radius curve and hiding its severity with a tunnel.

A 3rd radius curve will take a lesser 1040 mm to complete a 180-degree turn, leaving approximately 90 mm (3 1⁄2 in) on each side of the board. There's no doubt that's an improvement, but some sort of bone-shaped track plan along the leading edge of the board will probably still be required to create a credible scene.

For those modelling using a flexible track, 18" and 21" Tracksettas are the closest to 3rd and 4th radius curves respectively, although it should be noted these exhibit a slightly tighter radius than their Setrack counterparts.  

Whichever method or radius you use is your choice for your railway, but hopefully, you at least now have a better idea of what is and isn't possible.