What is a nominal wind load?

A nominal wind load is the unfactored, service-level wind pressure used in Allowable Stress Design (ASD). In ASCE 7-10 and later, the basic wind speed maps give ultimate (strength) values, so the nominal pressure is exactly 0.6 times the ultimate pressure. For example, a 40 psf ultimate pressure becomes a 24 psf nominal pressure.

How do I convert ultimate wind load to nominal wind load?

Multiply the ultimate (strength) pressure by 0.6 to get the nominal (service) pressure, so 40 psf becomes 24 psf. Because pressure is proportional to wind speed squared, the equivalent nominal speed is the ultimate speed times the square root of 0.6, about 0.775. A 150 mph ultimate speed becomes roughly 116 mph nominal.

Why are nominal wind loads multiplied by 0.6?

From ASCE 7-10 onward, the wind speed maps switched to ultimate (strength-level) speeds, while Allowable Stress Design needs service-level loads. The single 0.6 factor scales the ultimate pressure back down to nominal. In ASD load combinations, wind enters factored as 0.6W, which keeps the service-level magnitude consistent with the older nominal maps.

When are nominal wind loads used instead of ultimate loads?

Nominal (service-level) wind loads drive Allowable Stress Design checks. They are used in the everyday ASD load combinations as 0.6W paired with dead and live loads, and for serviceability checks like deflection and story drift. Ultimate (strength-level) loads, entered as 1.0W, are used instead in LRFD strength design.

What is the difference between nominal and ultimate wind speed?

Both describe the same wind event at two levels. The ultimate speed comes straight from the ASCE 7-10 and later maps and pairs with strength-level pressure and LRFD. The nominal speed is the service-level value, found by multiplying the ultimate speed by the square root of 0.6 (about 0.775), and pairs with reduced pressure and ASD.

ASCE 7-10+ · DESIGN METHODS

Nominal (Service-Level) Wind Loads

The unfactored, service-level wind pressure used in Allowable Stress Design — exactly 0.6 times the ultimate (strength) pressure in ASCE 7-10 and later.

ServicePRESSURE LEVEL

0.6×OF ULTIMATE PRESSURE

√0.6≈ 0.775 V_ult SPEED

0.6WASD LOAD COMBINATION

VIOLET · FROM ULTIMATE TO NOMINAL

One factor: multiply by 0.6

The strength-level (ultimate) pressure is scaled down to the service-level (nominal) pressure for ASD. Speed scales by the square root of the same factor.

Pressure × 0.6

Nominal pressure = 0.6 × ultimate pressure. Ultimate 40 psf becomes nominal 24 psf.

0.6 × ULTIMATE

Speed × √0.6

Because pressure scales with V², the equivalent nominal speed is V_ult × √0.6 ≈ 0.775 V_ult. Ultimate 150 mph → nominal ≈ 116 mph.

≈ 0.775 V_ult

VIOLET · WHERE NOMINAL APPLIES

Where service-level loads do the work

Nominal pressures drive the Allowable Stress Design checks — the everyday combinations, serviceability, and drift.

ASD Load Combinations

Wind enters the allowable-stress combinations factored as 0.6W, paired against dead and live loads.

D + 0.6W

Serviceability & Deflection

Deflection and serviceability limits are checked against service-level (nominal) wind, not the factored strength load.

SERVICE LEVEL

Story Drift

Lateral drift of a building under wind is evaluated at service level, where nominal loads set the sway you actually feel.

DRIFT CHECK

VIOLET · WORKED EXAMPLE

Ultimate to nominal in one step

Start from the strength-level (ultimate) values and apply the single 0.6 factor.

By Pressure

Ultimate: p_ult = 40 psf

Apply 0.6: 40 × 0.6 = 24 psf

Nominal: p_nom = 24 psf

40 psf → 24 psf

By Speed

Ultimate: V_ult = 150 mph

Apply √0.6: 150 × 0.775

Nominal: V_nom ≈ 116 mph

150 mph → 116 mph

Pressure and speed give the same answer because q is proportional to V²: 0.6 on pressure equals √0.6 ≈ 0.775 on speed. Both routes turn the 150 mph / 40 psf ultimate case into the 116 mph / 24 psf nominal case.

VIOLET · QUICK CONTRAST

Nominal vs ultimate at a glance

Same wind event, two pressure levels keyed to two design methods.

	Nominal (Service)	Ultimate (Strength)
Design method	ASD	LRFD
Pressure level	0.6 × ultimate	Full strength pressure
Wind in combinations	0.6W	1.0W
Example pressure	24 psf	40 psf
Example speed	≈ 116 mph	150 mph

Pre-ASCE 7-10 wind speed maps were already nominal (service-level). From ASCE 7-10 onward the maps switched to ultimate speeds, which is why the 0.6 / √0.6 conversion exists. See the full comparison for the terminology side by side.

Nominal vs Ultimate →

EMERALD · NEXT STEPS

Keep going on design methods

Compare the two pressure levels, then see how each one enters its load combinations.

Get Wind Load Calculators Design Methods Hub