Two multiplications, and why they are worth separating
Force is pressure times projected area. Moment is force times the height it acts at. That is the whole model, and the reason to write it out item by item rather than as one number is that the two terms behave differently as you change the installation.
Work the defaults through. A wind pressure of 25 pounds per square foot, an antenna of 8 square feet at 42 feet, and a 2 inch mast standing 20 feet above the base. The mast presents 2 divided by 12 times 20, which is 3.33 square feet. The antenna takes 25 times 8, so 200 pounds; the mast takes 25 times 3.33, so 83.3 pounds; the total is 283.3 pounds. For the moment, the antenna acts at 42 feet giving 8,400 ft-lb, and the mast acts as though all its area were at its mid-height of 10 feet, giving 833 ft-lb. Total 9,233 ft-lb.
Notice the asymmetry. The mast has 42 percent of the antenna area but produces under 10 percent of its moment, because it is low down. Height is worth more than area to a moment, and the practical consequence is that a small antenna raised another ten feet costs more than a slightly larger one at the same height.
Where the pressure has to come from
There is no wind speed field here, and that is deliberate. Converting a wind speed into a design pressure is not one equation — it involves the exposure of the site, the height above ground, the shape of what the wind is hitting, gust effects and the load factors the design method uses, and the resulting figure is set by the rules the jurisdiction has adopted and by the engineer applying them. A page that offered a speed-to-pressure box would be inviting you to treat a physics approximation as a code figure, which is precisely the error that gets people hurt.
So the pressure is an input, restated in the output, and taken from your engineer or from the requirement that applies to your site. What the calculator adds is the bookkeeping: which item contributes what, and how much each lever arm is worth.
Projected area is not the same as wind load
A flat panel and a round tube with the same projected area do not experience the same force, because shape changes how air separates around them. Design methods handle that with a shape or force coefficient, and manufacturers publish antenna wind areas in two different conventions: some give a bare projected area, some give an effective area that already has a coefficient folded in. Mixing the two sources in one calculation double-counts or under-counts by a large margin, and the only way to know which you have is to read what the manufacturer says the number means.
Ice is the other thing missing. A coating of ice increases the projected area of every member, adds weight, and does both at the time of year when the wind is worst. Where ice is a load case, it is a load case for an engineer and not for arithmetic.
Why there is no verdict here, and never will be
If you enter a rated wind area or a rated moment, this page prints it back exactly as you typed it and does not divide it into anything. That is not squeamishness. A published rating is established under stated conditions — a particular wind speed, exposure category, mounting arrangement and set of load factors — and the arithmetic above was performed under none of them. Dividing one by the other produces a number that looks like an answer and means nothing.
Whether a mast, a bracket, a roof mount, a base plate or a foundation will take these loads belongs to a structural engineer, to the manufacturer instructions for the specific product, and to the building department that issues the permit. The same is true of the guy design that would resist the force, of the anchors, and of the ground they sit in.
The consequence of getting it wrong is not a bent mast. A mast that lets go comes down across its whole fall radius, fast, and if a power line is in that radius the result is fatal — to whoever is holding it and often to anyone nearby. Clear fall radius in every direction, with margin, is the first thing to establish about any site, before any of this arithmetic matters. Tower climbing is specialist work with fall protection, and lightning protection and bonding for a raised metal structure is a standards-governed subject of its own.
Questions people ask
How do I calculate the wind load on an antenna mast?
Multiply the wind pressure by the projected area to get force, then multiply each force by the height it acts at to get the moment about the base. With 25 pounds per square foot, an 8 square foot antenna at 42 feet and a 2 inch mast 20 feet tall, the antenna takes 200 pounds and the mast 83.3, so 283.3 pounds total, and the moment comes to 9,233 ft-lb. Every one of those inputs is yours, and the result is arithmetic rather than an assessment.
Why does this page not convert wind speed into pressure?
Because that conversion is not a single equation you can safely put in a box. Turning a speed into a design pressure involves site exposure, height above ground, the shape of the object, gust effects and the load factors of the design method, and the figure that applies is set by the rules the jurisdiction has adopted and by the engineer applying them. Offering a speed field would invite you to treat an approximation as a code figure.
Is my mast rated for this load?
This page cannot tell you and does not try. If you enter a manufacturer rating it is printed back exactly as typed and is not compared with anything, because a published rating is established under stated conditions — a wind speed, an exposure, a mounting arrangement, load factors — and the arithmetic here was done under none of them. That comparison is engineering judgement and belongs to a structural engineer, the manufacturer instructions and the building department.
Does the mast itself matter, or just the antenna?
It matters for force and much less for moment. On the default figures the mast has 3.33 square feet against the antenna 8, so 42 percent of the area and 83.3 pounds of the 283.3 total. But it acts at its mid-height of 10 feet rather than at 42, so it contributes 833 ft-lb of the 9,233 — under a tenth. Long or wide masts and stacked arrays change that balance, which is why the page itemises rather than totalling.
Is the wind area the manufacturer publishes the same as projected area?
Not always, and the difference is large enough to matter. Some manufacturers publish a bare projected area, others publish an effective area that already includes a shape or force coefficient. Mixing conventions between an antenna from one source and a mast figure from another will over- or under-count. Read what the number is defined as before using it, and if the definition is not stated, ask rather than assume.