Geodesic Dome Calculator (2V Strut Lengths)

This calculator gives the strut lengths for a 2V geodesic dome, the simplest dome with two strut lengths. Enter the radius of the dome; you get the length of the A struts and the B struts (centre of hub to centre of hub) and the floor area of a hemisphere dome.

Formula

Strut length = chord factor × radius. For a 2V icosahedral dome the chord factors are A = 0.546533 and B = 0.618034. Floor area ≈ π r² (the real footprint of a 2V hemisphere is a decagon, a few percent smaller).

• r: radius from the centre of the floor to the hubs
• A hemisphere 2V dome uses 30 A struts and 35 B struts and 26 hubs.

Worked Example

A dome with a 10 ft radius.

1. A struts = 0.546533 × 10 = 5.465 ft
2. B struts = 0.618034 × 10 = 6.180 ft
3. Floor area = π × 10² = 314.2 ft²

How to read the result

The lengths are hub centre to hub centre. Subtract what your hub system needs (half the hub size at each end) before cutting, and cut one test triangle first. The A struts are the five that meet at the top and at each pentagon centre; the B struts form the hexagons.

Limits and common mistakes

• This page gives geometry only. A dome that people use needs a frame, covering and fixings designed for wind and snow where you live.
• Higher frequencies (3V, 4V) need more strut lengths and different factors.
• Use one unit throughout; the factors work in feet, metres or inches.

Frequently Asked Questions

How many struts does a 2V dome have?

65 for a hemisphere: 30 A struts and 35 B struts.

What is a chord factor?

The strut length for a sphere of radius 1; multiply by the radius.

Does the formula work in metres?

Yes. Enter the radius in metres and read the lengths in metres.

How tall is a 2V hemisphere dome?

About equal to its radius.

in rad | Dome radius | ft | 10 | 0 | 1000
out a | A strut length (30 per hemisphere) | ft | 0.546533 * rad | 3
out b | B strut length (35 per hemisphere) | ft | 0.618034 * rad | 3
out area | Floor area (circle, approx.) | ft² | pi * rad^2 | 1