Effective Projected Area Calculator
Effective projected area, or EPA, is the area a fixture, sign or structure presents to the wind after its shape is accounted for. Lighting poles, sign supports and antennas are rated by EPA because wind pressure multiplied by EPA is what produces the force the support has to resist. This calculator covers three related jobs in separate tabs: a shape-based EPA with wind angle and blockage, the standard wind-load EPA used for poles and luminaires, and the antenna effective aperture that shares the same name.
Quick Answer
For a rectangular sign panel 3 m by 1.5 m, hit by wind at 30 degrees with 10% blockage, the actual projected area is 4.5000 m² and the effective projected area is 3.5074 m², a projection efficiency of 77.94%. In the wind-load tab, a 300 m² face with a drag coefficient of 0.75 gives an EPA of 225.00 m².
Key takeaways
- Wind-load EPA is frontal projected area times drag coefficient. That is the figure pole and luminaire makers publish, usually in square feet.
- The shape tab answers a different question: how much of a shape's silhouette survives a tilted wind and partial blockage. It does not apply a drag coefficient except in the vehicle row, where Cd is part of the shape step.
- EPA on its own is not a force. Multiply it by the design wind pressure for the site to get the load the support must resist.
- Antenna effective aperture uses the same words for a receiving area derived from gain and wavelength. Never mix it into a wind calculation.
- Quick Answer
- How to use this effective projected area calculator
- The three EPA formulas, and what each one is for
- Worked examples: a sign panel, a building face and a dish
- Drag coefficients: what to enter when no measured value exists
- The antenna meaning: effective aperture from gain and wavelength
- What competing calculators miss
- Honest limits before you size a pole from this page
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use this effective projected area calculator
Pick the tab that matches the job, enter the figures for that tab, then click Calculate. Results stay hidden until you do.
- Shape-based EPA: choose the shape, enter its dimensions, then the incident angle and blockage factor. You get actual area, effective area, projection efficiency and solidity ratio.
- Wind-load EPA: enter the frontal projected area and the drag coefficient. This is the tab to use for a luminaire, sign or bracket going on a pole.
- Antenna aperture: enter frequency in GHz and gain in dB. You get wavelength, linear gain and effective aperture.
Keep length units consistent inside any one calculation. Metres give square metres, feet give square feet, and pole catalogues in the United States almost always quote EPA in square feet.
The three EPA formulas, and what each one is for
Each tab uses a different formula because each one solves a different problem. Reading the wrong one into a design is the most common EPA mistake.
Wind-load EPA = Frontal Projected Area × Drag Coefficient
Antenna effective aperture = λ² × G ÷ (4π), where λ = c ÷ f and G = 10^(gain in dB ÷ 10)
The wind-load formula is the standard for lighting and sign supports. Manufacturer guidance on luminaire EPA, such as the EPA calculation note for luminaires, defines EPA exactly this way, and the Axis white paper on effective projected area makes the same point: EPA combines the two surroundings-independent factors, Cd and A, so one fixture can be checked against different wind speeds later. The structural practice behind it sits in the AASHTO specifications for sign, signal and lighting supports and in ASCE 7 wind provisions.
The shape formula is geometry. A tilted flat surface presents less area to the flow, and the reduction follows the cosine, the same relationship a cosine calculator evaluates: at 30 degrees you keep 86.60% of the head-on area, at 60 degrees 50%, and at 90 degrees, edge-on, nothing. Blockage then removes the obstructed share directly.
| Shape in the tool | Actual projected area used | Note |
|---|---|---|
| Rectangle | Length × Width | Sign panels, boards, flat faces |
| Circle / Sphere | π × (Diameter ÷ 2)² | Both project as a circle |
| Ellipse | π × (Major ÷ 2) × (Minor ÷ 2) | Enter full axes, not semi-axes |
| Cylinder (side-on) | Diameter × Height | How a pole section is counted |
| Cone (side-on) | 0.5 × Base Diameter × Height | Projects as a triangle |
| Vehicle / Aircraft | Front Area × Cd | Cd is applied inside the shape step here |
| Building | Width × Height × Shape Factor | Shape factor runs 1.0 down to 0.6 streamlined |
Worked examples: a sign panel, a building face and a dish
The pre-filled values reproduce all three examples exactly, so you can check the tool before trusting it on your own figures.
| Example | Inputs | Result |
|---|---|---|
| Shape: sign panel at an angle | 3 m × 1.5 m, 30°, 10% blockage | Actual 4.5000, effective 3.5074, efficiency 77.94%, solidity 0.9000 |
| Shape: pole section side-on | Cylinder 0.3 m × 6 m, 30°, no blockage | Actual 1.8000, effective 1.5588, efficiency 86.60% |
| Wind-load: building face | Frontal area 300 m², Cd 0.75 | EPA 225.00 m² |
| Wind-load: floodlight check | Frontal area 2.09 ft², Cd 1.20 flat plate | EPA 2.51 ft² (shown as 2.51 in the tool's m² label) |
| Antenna: dish | 10 GHz, 30 dB gain | λ 0.0300 m, linear gain 1000.00, aperture 0.0715 m² |
How fast the angle eats area, for any flat shape with no blockage:
A pole assembly is a sum, not a single fixture. Add the EPA of every luminaire, bracket and accessory, each times its quantity, then compare the total with the pole's maximum allowable EPA at your site's wind speed. Guidance such as the light pole wind speed and EPA explainer stresses matching that total to the pole's EPA curve at the local design wind speed, not to the headline mph figure alone.
Drag coefficients: what to enter when no measured value exists
Cd is a dimensionless shape factor, not a property of the material. Higher means the shape pushes harder against the wind for the same frontal area.
| Body type (luminaire practice) | Assumed Cd | Use when |
|---|---|---|
| Flat plate body | 1.20 | Boxy fixtures and flat signs, worst-case default |
| Angled body | 1.00 | Tilted or faceted housings |
| Spherical body | 0.85 | Rounded or globe-style fixtures |
Those assumed values come from the luminaire EPA note cited above, used because most projects have no wind-tunnel figure for a specific fixture. When a manufacturer publishes an EPA for the exact fixture and mount, use it directly instead of rebuilding it from area and Cd. A crosswind calculator shows the related geometry for vehicles: only the wind component perpendicular to travel does the pushing.
The antenna meaning: effective aperture from gain and wavelength
An antenna's effective aperture is how large it acts as a receiver. The relation Aeff = λ²G ÷ (4π) is a standard result in antenna theory, set out in references such as VRC Academy's effective aperture notes, which also stress that aperture scales with the square of the wavelength: drop the frequency and the same gain captures far more area.
That scaling surprises people the first time. The 10 GHz dish in the example, with a strong 30 dB of gain, has an effective aperture of only 0.0715 m². Run a 2.4 GHz antenna at 15 dB in the same tab and you get a wavelength of 0.1249 m, linear gain of 31.62 and an aperture of 0.0393 m². For antenna length and element sizing rather than aperture, a dipole antenna calculator works from the same wavelength in the opposite direction.
What competing calculators miss
Single-formula tools dominate this search. Each one does a slice of the job well and leaves the rest to guesswork.
- One meaning only: the best-known EPA tools compute frontal area times Cd and stop. Antenna pages compute aperture and stop. Nobody else puts the geometric shape version, with angle and blockage, beside both of them.
- No angle or blockage: a tilted sign or a partly shielded fixture gets the same answer as a head-on, fully exposed one in a two-input tool. Real installations are rarely head-on.
- No path to force: several tools present EPA as if it were the final load. It is an area. The force step, pressure times EPA, and the pole-assembly sum are explained here because that is what the number is bought for.
- Unexplained drag values: tools that ask for Cd rarely say what to enter for a common fixture shape. The assumed-value table above gives a defensible starting point and says when to override it with a published figure.
Honest limits before you size a pole from this page
This calculator computes EPA. It does not compute wind pressure, gust factors, height and exposure coefficients, or the structural check itself, and it does not sum a multi-fixture assembly for you. Those steps belong to ASCE 7, the AASHTO support specifications and the pole manufacturer's tables. Have a licensed engineer sign off any support over a public space. Antenna results are not a link budget.
Frequently asked questions
In wind engineering, EPA is the area an object presents to the wind after its shape is accounted for, most commonly frontal projected area multiplied by the drag coefficient. Lighting poles, signs and luminaires are rated by EPA. In antenna theory, the same words mean effective aperture, the receiving area derived from gain and wavelength. This page keeps the two meanings on separate tabs.
Find the fixture's frontal projected area, the largest silhouette of the fixture and its mount as installed, and multiply by its drag coefficient in the Wind-load EPA tab. Then add the EPA of every fixture, bracket and accessory on the pole, each times its quantity, and compare the total with the pole's maximum allowable EPA at your design wind speed.
When no measured value exists, luminaire practice assumes 1.20 for a flat plate body, 1.00 for an angled body and 0.85 for a spherical body. Use a manufacturer's published EPA instead whenever one exists for the exact fixture and mount, because it already contains the right coefficient for that shape.
A tilted surface presents less area to the wind, reduced by the cosine of the angle. At 30 degrees you keep about 86.6 percent of the head-on area, at 60 degrees 50 percent, and at 90 degrees the surface is edge-on and the projected area is zero. The verdict badge in the results restates that as projection efficiency.
Actual projected area is pure geometry: the shape's silhouette, such as 3 m times 1.5 m equals 4.5000 square metres for the worked sign panel. Effective projected area adjusts it, by angle and blockage in the shape tab, or by the drag coefficient in the wind-load tab. For the panel at 30 degrees with 10 percent blockage, the effective area is 3.5074 square metres.
No. EPA is an area, measured in square metres or square feet. Force is wind pressure times area, so multiply EPA by the design wind pressure for your site, height and exposure. This calculator stops at EPA; pressure and the structural check follow your local code and the pole manufacturer's tables.
They are linked by Aeff equals lambda squared times G divided by 4 pi. A higher-gain antenna has a larger effective aperture at the same wavelength, and at a higher frequency the wavelength shrinks, so the aperture shrinks for the same gain. At 10 GHz and 30 dB, the result here is 0.0715 square metres.
Keep length units consistent and the area comes out in the square of those units: metres give square metres, feet give square feet. United States pole and luminaire catalogues usually quote EPA in square feet. For the antenna tab, enter frequency in GHz and the aperture is returned in square metres.
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References
- TEB / Hydrel. EPA Calculation for Luminaires. Accessed October 21, 2026.
- Axis Communications. Effective Projected Area (EPA). Accessed October 21, 2026.
- LED Light Expert. Light Pole Wind Speed Ratings and EPA Explained. Accessed October 21, 2026.
- Lumenpulse. EPA and the ABCs of Wind Safety. Accessed October 21, 2026.
- ZGSM. Effective Projected Area and Static Load Test for Outdoor Luminaires. Accessed October 21, 2026.
- VRC Academy. Effective Aperture Calculator and Antenna Theory Notes. Accessed October 21, 2026.