Wind Load Calculator — ASCE 7-22 Velocity Pressure and Wall Design Pressure

Background.

A wind load calculator answers a question that every deck ledger, sign frame, shear wall and metal building runs into: how many pounds per square foot is the wind actually pushing on this surface, and how many pounds is that in total? In the United States the answer comes from ASCE/SEI 7, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, and it is not simply half rho vee squared. It is a chain of factors, each of which represents something real about the site and the building, and each of which has a table behind it.

The chain starts with the basic wind speed V. That is a 3-second gust speed, mapped by ASCE for a specific Risk Category — a hospital and a storage shed do not get the same map — and it is the one input this page will never guess for you. Take it from the ASCE 7 Hazard Tool or from the map adopted in your jurisdiction. Everything downstream scales with the square of it, so a 10 percent error in V is a 21 percent error in the answer.

V is then converted into a velocity pressure by ASCE 7-22 Eq. 26.10-1: qh equals 0.00256 times Kz times Kzt times Ke times V squared, in pounds per square foot. Kz is the velocity pressure exposure coefficient, and it encodes the fact that wind slows down near rough ground: over open terrain at 30 feet it is 0.98, but in a built-up suburb at the same height it is 0.70. Kzt is the topographic factor, which is 1.0 on flat or rolling ground and greater only near the crest of an isolated hill, ridge or escarpment. Ke is the ground elevation factor, exp of minus 0.0000362 times the elevation in feet — thinner air at altitude means less pressure, and it is always permissible to ignore it by using 1.0.

The velocity pressure is not yet a load. Turning it into one takes three more numbers. Kd, the wind directionality factor, is 0.85 for a building and accounts for the low probability that the worst wind direction coincides with the worst structural direction. G, the gust-effect factor, is 0.85 for a rigid building — one whose fundamental frequency is at least 1 hertz, which covers nearly everything low-rise. And Cp, the external pressure coefficient, is where the shape of the building enters: the windward wall gets +0.8, the side walls get −0.7, and the leeward wall gets somewhere between −0.5 and −0.2 depending on how long the building is in the wind direction. Then the internal pressure coefficient (GCpi) is added or subtracted, because a building with air inside it is a pressure vessel as well as an obstacle, and both signs must be checked.

One detail on this page is worth reading before you trust the number. ASCE 7-22 moved Kd out of the velocity pressure equation and into the pressure equations, where ASCE 7-16 had kept it inside. The velocity pressure reported here therefore excludes Kd, which is the 7-22 convention; if you are working from ASCE 7-16, multiply it by 0.85 to get the qh your edition prints. The design pressure is numerically identical under either arrangement, and several secondary sources online still print the 7-16 form under a 7-22 heading.

What this page covers, it covers exactly. It computes wall pressures for the main wind force resisting system under the Chapter 27 Directional Procedure. It does not compute roof pressures or uplift, which need the roof half of Fig. 27.3-1 and turn on roof angle, on the ratio h/L and on zone. It does not compute components-and-cladding pressures, which need (GCp) values from Fig. 30.3-1 onward that vary with zone and with effective wind area — so it will not size a window mullion or a roof fastener pattern. It evaluates every surface at qh, the velocity pressure at mean roof height, where ASCE 7-22 evaluates the windward wall at qz, which grows with height; that is conservative rather than unconservative, but it is materially conservative above roughly 60 feet, where the wall should be taken level by level instead.

ASCE 7 is a standard, not a law. It becomes binding through adoption — IBC 2021 §1609.1.1 points wind design at it — and local amendments govern. The edition in force where you are building may be ASCE 7-16 or older, and the adopted wind map may not be the current one. Wind is also the load case that most often decides whether a building stays standing in a hurricane or a derecho, and it is exactly the case where a plausible-looking wrong number does the most damage. Treat what this page returns as a design starting point that a licensed structural engineer must confirm and sign off before work proceeds.

What is wind load calculator?

Wind load is the pressure that moving air exerts on a surface, expressed in pounds per square foot, together with the total force that pressure produces over an area. It is not one number for a building: the windward face is pushed inward while the leeward and side faces are pulled outward by suction, and a roof is usually being sucked upward rather than pressed down. That is why hurricane damage so often begins with a roof leaving and not with a wall caving in.

ASCE 7 splits the calculation into two halves. Chapter 26 turns a mapped wind speed into a velocity pressure q by applying site factors: terrain roughness through Kz, topography through Kzt, and air density through the ground elevation factor Ke. Chapter 27 then turns q into a design pressure p on a specific surface by applying the directionality factor Kd, the gust-effect factor G, an external pressure coefficient Cp that depends on which face you are looking at, and an internal pressure coefficient (GCpi) that depends on how leaky the building is.

The distinction between the main wind force resisting system and components and cladding matters more than most people expect. The MWFRS is the skeleton — the shear walls, diaphragms and frames that carry the whole building's wind force down to the foundation — and it sees pressures averaged over large areas. Components and cladding are individual pieces: a window, a fastener, a purlin, a soffit panel. They see much higher local peaks, especially at corners and edges, and they are governed by a different chapter with different coefficients. This page computes MWFRS wall pressures. Sizing a fastener from an MWFRS pressure is one of the most common and most dangerous errors in wind design, which is why it is stated here and beside the result rather than in an FAQ.

How to use this calculator.

1. 01Get the basic wind speed V for your exact site first, from the ASCE 7 Hazard Tool or the map adopted in your jurisdiction, and make sure it is for the right Risk Category. This is the only input the calculator cannot help you with, and it is the one that matters most because the pressure scales with V squared.
2. 02Choose the exposure category honestly. Exposure B requires closely spaced obstructions over a long upwind fetch in every direction that matters; a house on the edge of a subdivision facing an open field is Exposure C on that side. Choosing B when C applies understates the pressure by about 30 percent at 30 feet.
3. 03Enter the mean roof height — the average of eave and ridge — not the ridge height, and not the wall height.
4. 04Enter the site's ground elevation if you know it. If you do not, leave it at 0: Ke = 1.0 is always permitted and is conservative.
5. 05Leave Kzt at 1.0 unless the building sits on or near the crest of an isolated hill, ridge or escarpment. If it does, the factor comes from ASCE 7-22 Fig. 26.8-1 and this page will not compute it for you.
6. 06Leave G at 0.85 unless the building is flexible — fundamental natural frequency below 1 hertz. Almost every low-rise building is rigid.
7. 07Set the enclosure classification carefully. Partially enclosed is not a synonym for draughty; it is a specific classification for a building with a large dominant opening, and it triples the internal pressure from ±0.18 to ±0.55. An open building such as a canopy carries no internal pressure at all.
8. 08Enter L/B — the plan dimension parallel to the wind divided by the one across it. It changes the leeward coefficient and nothing else.
9. 09Pick the surface. Design a single wall by choosing that wall; size a shear wall or a lateral system by choosing the net across the building, where the internal pressure cancels and the combined coefficient is larger.
10. 10Read the result together with the note beside it, then take both, the code edition adopted in your jurisdiction, and the roof and cladding cases this page does not cover, to a licensed structural engineer for sign-off.

The formula.

The calculation runs in two stages, and every constant in it comes from a numbered table.

Stage one is the velocity pressure. ASCE 7-22 Eq. 26.10-1 reads qh = 0.00256 × Kz × Kzt × Ke × V², with V in miles per hour and qh in pounds per square foot. The leading constant folds in standard air density and the unit conversion from mph squared to psf. Kz comes from note 1 to Table 26.10-1 as Kz = 2.01 (z/zg)^(2/α), evaluated at the mean roof height and floored at 15 feet, with the terrain exposure constants α and zg from Table 26.11-1: 7.0 and 1200 feet in exposure B, 9.5 and 900 feet in C, 11.5 and 700 feet in D. Ke is exp(−0.0000362 × elevation) from Table 26.9-1. Kzt is 1.0 unless the site is on a hill.

For the worked example on this page — 115 mph, exposure C, 30 feet, sea level, flat ground — Kz works out to 2.01 × (30/900)^(2/9.5) = 0.9823, which is exactly the 0.98 that Table 26.10-1 prints at 30 feet in exposure C. Ke is 1.0. So qh = 0.00256 × 0.9823 × 1 × 1 × 115² = 33.2551 psf.

Stage two turns that into a surface pressure. ASCE 7-22 Eq. 27.3-1 is p = q·Kd·G·Cp − q·Kd·(GCpi). Kd is 0.85 for a building, from Table 26.6-1. G is 0.85 for a rigid building, permitted by §26.11.1. Cp comes from Fig. 27.3-1: +0.8 on the windward wall regardless of building proportions, −0.7 on the side walls, and −0.5, −0.3 or −0.2 on the leeward wall at L/B of 0 to 1, exactly 2, or 4 and above, with linear interpolation permitted between those points and used here.

On the windward wall of the example: 33.2551 × 0.85 × 0.85 × 0.8 = 19.2215 psf of external pressure. The internal term is where the sign convention earns its keep. (GCpi) is ±0.18 for an enclosed building and both signs must be checked. On a windward wall the external pressure pushes inward, so the case that loads the wall hardest is internal suction, which pulls it inward as well: the term adds, at 33.2551 × 0.85 × 0.18 = 5.0880 psf. The design pressure is 19.2215 + 5.0880 = 24.3095 psf, and over 300 square feet that is 7,292.85 pounds.

On the leeward wall of the same building the sign flips throughout. Cp is −0.5 at L/B = 1, giving an external term of −12.0134 psf, and the governing internal case is now pressurisation pushing outward, so the internal term is −5.0880 psf and the design pressure is −17.1015 psf of suction. Note that the leeward wall is being pulled off the building at roughly 70 percent of the pressure pushing on the windward wall — wind design is not only about the face the wind hits.

The net-across-the-building mode is the one that surprises people. When the same cross-section is taken as a whole, the internal pressure acts inward on one wall and outward on the other and cancels exactly, so it disappears — not by assumption, by arithmetic. The combined coefficient is 0.8 + 0.5 = 1.3, giving 33.2551 × 0.85 × 0.85 × 1.3 = 31.2349 psf and 9,370.47 pounds over the same 300 square feet. That figure, not the 24.31 psf of the windward wall alone, is what a lateral force-resisting system has to carry.

Nothing on this page rounds an intermediate value. All arithmetic is carried at 40 significant digits and rounded once, at the point the numbers are handed to the display. The two piecewise rules — the 15-foot floor on Kz and the leeward interpolation on L/B — switch on the unrounded input, and each of their breakpoints is tested immediately below, exactly at, and immediately above.

A worked example.

Frequently asked questions.

References& sources.

1. [1]ASCE/SEI 7-22, Minimum Design Loads and Associated Criteria for Buildings and Other Structures — the primary source for every equation, table and figure on this page: Eq. 26.10-1 (velocity pressure), Table 26.6-1 (Kd = 0.85 for buildings), Table 26.9-1 (Ke = exp(−0.0000362 z)), Table 26.10-1 note 1 (Kz closed form), Table 26.11-1 (terrain exposure constants α and zg), §26.11.1 (G = 0.85 for rigid buildings), §26.12 (enclosure classification), Table 26.13-1 ((GCpi) = ±0.18 / ±0.55 / 0.00), Fig. 27.3-1 (wall external pressure coefficients) and Eq. 27.3-1 (design pressure). Authority: ASCE/SEI. Document revision: ASCE/SEI 7-22. Access: gated — the standard's text sits behind ASCE's paywall, so every figure attributed to it here is corroborated by at least two open reproductions listed below. Independence: primary. Retrieved 2026-07-29.
2. [2]ASCE 7 Hazard Tool — the authoritative lookup for the basic wind speed V at a specific latitude and longitude, by ASCE 7 edition and Risk Category. This page requires the user to supply V from here or from the locally adopted map and never guesses it. Authority: ASCE/SEI. Document revision: live service covering ASCE 7-16 and 7-22. Locator: wind hazard by site coordinates. Access: open in a browser (registration prompted for saved reports); it is a client-rendered application and refuses automated retrieval (HTTP 403 on 2026-07-30). Independence: primary. Retrieved 2026-07-29.
3. [3]MECA Enterprises, 'ASCE 7-22 Wind Load Changes' — documents that the directionality factor Kd was moved out of the velocity pressure equation and into the design pressure equations in ASCE 7-22, describes it as a technical change with no impact on loading in this edition, and explains the motivation (separate Kd values for internal and external pressure in future editions, and a distinct KdT for the new tornado provisions). This is the source for the edition conflict recorded on the page and in the dossier. Authority: MECA Enterprises (wind engineering software vendor). Document revision: ASCE 7-22 change summary. Access: open. Independence: secondary-check. Retrieved 2026-07-29.
4. [4]Carlisle SynTec Systems, 'Adjustments Between ASCE 7-16 and ASCE 7-22' (SpecTopics, 20 February 2025) — an independent confirmation of the Kd relocation, of the unchanged internal pressure coefficients (0.18 enclosed, 0.55 partially enclosed), and of the change in wind speed map sets between the two editions. Authority: Carlisle SynTec Systems. Document revision: 2025-02-20. Access: open. Independence: secondary-check. Retrieved 2026-07-29.
5. [5]Bentley Systems, STAAD.Pro Help v18, verification example 'V. ASCE 7-16 Wind Load Generation on Building' — the independent check for this page (BUILD-BRIEF §10.5). Its published result for V = 108 mph, ground elevation 230 ft, mean roof height 40 ft, exposure B and Kzt = 1 is Kz = 0.761 and q = 19.14 lb/ft². This module returns Kz = 0.760609 and, once Kd is folded back in for the ASCE 7-16 arrangement, q = 19.1448 lb/ft². Result: agree, to three decimal places on Kz and four significant figures on q. Both values are asserted in wind-load.test.ts. Authority: Bentley Systems. Document revision: STAAD.Pro Help v18. Access: open. Independence: primary check. Retrieved 2026-07-29.
6. [6]The Structural World, 'Guide to Wind Load Analytical Procedure of ASCE 7-10' (7 February 2019) — an open reproduction of the wall external pressure coefficients from Fig. 27.4-1/27.3-1 (windward +0.8 at qz; leeward −0.5 / −0.3 / −0.2 at L/B of 0–1 / 2 / ≥4 at qh; side wall −0.7 at qh), of G = 0.85 for rigid buildings, and of the terrain exposure constants α = 7 / zg = 1200 ft (B), 9.5 / 900 ft (C) and 11.5 / 700 ft (D) with Kz = 2.01 (z/zg)^(2/α). Used to corroborate the gated primary text. Authority: The Structural World. Document revision: ASCE 7-10, unchanged in these particulars through 7-22. Access: open. Independence: secondary-check. Retrieved 2026-07-29.
7. [7]International Building Code 2021, §1609 'Wind Loads' — the adoption path that makes ASCE 7 legally operative: §1609.1.1 directs wind design to ASCE 7 and §1609.3 governs the basic wind speed. This is the basis for the statement beside the result that ASCE 7 is a standard rather than a law, that the adopted edition varies by jurisdiction, and that local amendments govern. Authority: International Code Council. Document revision: IBC 2021. Locator: §1609.1.1, §1609.3. Access: free to read on ICC Digital Codes in a browser, but automated retrieval is refused (HTTP 403 on 2026-07-30), so no value here is attributed to its text. Independence: secondary-check. Retrieved 2026-07-29.