What is the 3-second gust wind speed in ASCE 7?

The 3-second gust is the peak wind speed averaged over a 3-second window, measured at a 33 ft (10 m) reference height over open Exposure C terrain. It is the averaging basis ASCE 7 has used for the basic wind speed V since ASCE 7-95, captured as the highest 3-second average in the record rather than an instantaneous spike or long sustained mean.

How is the 3-second gust different from a sustained hurricane wind speed?

They average over very different time windows, so the same storm reads as different numbers. A reported sustained or 1-minute hurricane wind is averaged over roughly a minute and reads notably lower than a 3-second gust. You cannot convert one to the other with a fixed ratio because exact factors depend on terrain, storm type, and height, requiring engineering analysis.

What wind speed should I use for ASCE 7 wind load design?

Use the mapped 3-second gust basic wind speed V for your site, read from the current ASCE 7 maps. Never substitute a sustained, reported, or fastest-mile wind speed. Your risk category determines which speed map you read V from, since higher risk categories use maps with longer return periods. Actual mph values vary by location.

How does the 3-second gust feed into wind load calculations?

The mapped 3-second gust V is the starting point for velocity pressure, computed as qz = 0.00256 x Kz x Kzt x Kd x Ke x V squared, with the wind directionality factor Kd = 0.85 for buildings. Because every ASCE 7 map shares the same 3-second gust at 33 ft in Exposure C basis, qz and every load derived from it are computed on consistent terms nationwide.

Why did ASCE 7 switch from fastest-mile to 3-second gust wind speed?

ASCE 7 adopted the 3-second gust starting with ASCE 7-95, replacing the older fastest-mile metric used in pre-1995 U.S. codes. The fastest-mile averages over the time it takes one mile of air to pass, a longer and speed-dependent window that yields a lower number. The 3-second gust gives a consistent, directly comparable basis for every U.S. wind-speed map.

ASCE 7 · BASIC WIND SPEED BASIS

The 3-Second Gust Wind Speed

The averaging basis ASCE 7 has used for basic wind speed V since ASCE 7-95: the peak gust averaged over 3 seconds, read at a fixed reference height in open terrain.

3 secPEAK GUST AVERAGE

33 ftREFERENCE HEIGHT (10 m)

Exp. COPEN-TERRAIN BASIS

WHAT THE NUMBER REPRESENTS

A peak gust, averaged over a 3-second window

Wind speed fluctuates constantly. ASCE 7 captures the highest 3-second average within the record, not the instantaneous spike and not the long sustained mean.

The basic wind speed V on an ASCE 7 map is the peak of the 3-second average — higher than the sustained mean, lower than a single instantaneous spike.

THE STANDARD DEFINITION

How the gust speed is measured

Three fixed conditions make every ASCE 7 wind-speed map directly comparable across the country.

3-Second Average

The peak gust averaged over a 3-second duration — the basis ASCE 7 has used since ASCE 7-95.

3 SECONDS

33 ft Reference Height

Measured at 33 feet (10 meters) above ground — the standard anemometer reference height.

33 FT · 10 M

Exposure C Terrain

Defined over open terrain (Exposure C) — flat, unobstructed ground, the neutral mapping baseline.

OPEN TERRAIN

CONTEXT · QUALITATIVE

3-second gust vs other wind metrics

Different metrics average over different windows, so the same storm reads as different numbers. Longer averaging always yields a lower figure than the 3-second gust.

Metric	Averaging window	Where you see it	Relative to 3-sec gust
3-Second Gust	3 seconds	ASCE 7 basic wind speed V (U.S. design)	Baseline — the design reference
Fastest-Mile	Time for one mile of air to pass (speed-dependent)	Pre-1995 U.S. codes	Longer average → lower number
Sustained / 1-Minute	About one minute	Hurricane advisories, weather reports	Much longer average → notably lower number

Not the same as a sustained hurricane wind

A "Category 4, 150 mph" advisory reports a sustained wind, not a 3-second gust. Because the two average over very different windows, you cannot read one as the other — and exact conversion factors depend on terrain, storm type, and height, so they require engineering analysis rather than a fixed ratio.

WHY IT MATTERS FOR DESIGN

One basis, consistent loads nationwide

Every ASCE 7 wind-speed map is built on the same 3-second gust at 33 ft in Exposure C. Because the basis is fixed, the velocity pressure q_z — and every wind load derived from it — is computed on consistent terms whether you design in Florida, the Plains, or the Pacific Northwest. Use the mapped 3-second gust value as your starting point; never substitute a sustained or reported wind speed.

KEEP GOING

Put the right wind speed to work

Pull your site's basic wind speed from the current ASCE 7 maps, then size loads with confidence.

Open the Wind Load Calculators View ASCE 7-22 Maps