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Antenna mast wind load and guying calculator

Work out how hard the wind pushes on your antenna and mast, the bending force at the base, and the guy wires needed to hold it, so you can choose a mast and guys with a margin of safety.

A strong gale is about 55 mph, gusts in UK storms 80 to 100 mph
From the antenna's specification
Two thirds of the height is common
At least half the attachment height
Wind pressure––
Total wind force––
Base bending moment––
Guy tension––
Guy length––
Guy breaking strength––

These are estimates for planning. They assume three guys at 120°, a pinned mast base and steady wind. For permanent or tall installations, follow the mast maker's limits and get structural advice where needed.

The diagram updates as you change the values.

How wind load is worked out

Wind pressure rises with the square of the wind speed: q = ½ × air density × speed². At 80 mph that's about 780 newtons per square metre. Multiply by the antenna's wind area, which manufacturers quote, and by the mast's projected area times a drag factor of 1.2 for a round tube, to get the force. Because the antenna sits at the top, its force has a long lever arm, so the bending moment at the base is usually the limiting factor for an unguyed mast.

Guying

Guys turn that bending into tension in the wires and compression in the mast. The worst case is wind blowing straight towards one guy, which then carries almost all the load. A shallow guy angle, with anchors further out, reduces the tension. Anchors at a distance of 0.6 to 0.8 times the attachment height are a good compromise, giving a guy angle of about 50 to 60°. Use a guy material with a breaking strength well above the working load, and pre-tension the guys to about 10% of their breaking strength.

Practical points

  • Non-conductive guy rope such as Kevlar or polyester avoids interaction with your antennas. Steel guys near antennas should be broken up with insulators.
  • Telescopic masts often have a maximum wind area at full height. Stay well inside it, or lower the mast in storms.
  • Check local planning rules for permanent masts.

For the antenna dimensions themselves, see the Yagi and Moxon calculators.

Questions

How do I calculate wind load on an antenna?

Force = ½ × 1.225 × wind speed² × wind area, with speed in m/s and area in m². The calculator adds the mast and works out the bending moment.

How far out should guy anchors be?

Usually 0.6 to 0.8 times the height where the guys attach. Closer anchors greatly increase the tension.

What guy rope should I use?

UV-stable polyester or Kevlar rope is popular because it doesn't affect antennas. Choose a breaking strength at least 2.5 times the calculated tension.

What wind speed should I design for?

In the UK, gusts of 80 to 100 mph happen in severe storms, and more on exposed hills and coasts.