📏 Track Length Calculator
Add each straight segment's length and each curve's radius and arc angle to calculate the total track length for your layout — useful for estimating flex track or sectional track needs.
Straight Segments
Curved Segments
Straights added, curves worked out as arcs
Straight rows are simply summed. Each curve row is a slice of a circle of the radius you give it:
arc length = 2 x pi x radius x (angle / 360)
total = sum of straights + sum of arcs
18 in radius, 90 deg = 2 x pi x 18 x 0.25 = 28.3 in
18 in radius, 180 deg = 56.5 in
24 + 24 + 56.5 = 104.5 in = 8.71 ftThose are the three rows the tool starts with - the two ends of a simple oval would need a second 180 degree curve. Radius is measured to the centreline, and a full circle is a single row at 360 degrees.
Turning inches into a shopping list
The total is centreline running length, which is not the same as what you buy:
- Flex track comes in 3 ft lengths in HO, so divide by 36 and round up. Add 10 to 15 per cent - the offcut left after a curve is rarely long enough to use elsewhere.
- Sectional curves are sold by the piece, not the inch. An 18 in radius HO curve is normally a 30 degree section, so a half circle takes six of them and a full circle twelve.
- Turnouts are not in the figure. Each replaces roughly its own length of plain track, so count them separately and take that length off the straights.
Frequently asked questions
How long is a 90 degree curve at 18 inch radius?
28.3 inches - a quarter of the 113.1 inch circumference of an 18 inch radius circle.
How much flex track do I need for a 4x8 oval?
An oval of two 30-inch straights and two 18-inch radius half circles runs about 173 inches, or 14.4 feet - five 3-foot sections with a little spare.
Is the radius measured to the rail or the centre of the track?
To the centreline, which is how sectional track and templates are specified too. Measuring to a rail head gives you an answer half a track width out.