What is the difference between nominal and ultimate wind loads?

Ultimate wind loads are strength-level values read directly off the ASCE 7 basic wind-speed map (since ASCE 7-10) and used in LRFD with a 1.0W factor. Nominal wind loads are the service-level equivalent used in ASD, equal to the ultimate pressure multiplied by 0.6. It is one calculation expressed at two reference levels.

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

Multiply the ultimate (strength-level) pressure by 0.6 to get the nominal (service-level) pressure. Because pressure varies with the square of speed, the equivalent wind speed ratio is the square root of 0.6, about 0.775. So a 150 mph ultimate speed corresponds to roughly 116 mph nominal. Never apply the 0.6 factor twice.

Which wind load do I use for ASD versus LRFD?

LRFD (strength design) uses the ultimate wind load with a 1.0W load factor for member strength checks. ASD (allowable stress design) uses the nominal wind load, equal to 0.6 times the ultimate pressure, for service-level checks such as drift, deflection, and design pressure ratings. Both come from the same mapped ASCE 7 wind speed.

Is the nominal wind speed always 0.775 times the ultimate speed?

Yes. The nominal pressure is fixed at 0.6 times the ultimate pressure (the ASD load factor on W). Since velocity pressure scales with the square of speed, the equivalent speed ratio is the square root of 0.6, approximately 0.775. For example, 150 mph ultimate equals about 116 mph nominal. The actual mapped mph varies by site and risk category.

ASCE 7-10 · 7-16 · 7-22 · DESIGN METHODS

Nominal vs Ultimate Wind Loads

Q: Why did ASCE 7-10 change the wind-speed maps to ultimate values?

Through ASCE 7-05 the printed maps were nominal (service-level), and LRFD applied a 1.6W factor to reach strength. Starting with ASCE 7-10 the maps were re-cast as ultimate (strength-level) speeds, so LRFD now uses 1.0W directly and ASD recovers the service level with 0.6W. The design intent is unchanged; only the reference level moved.

Since ASCE 7-10, mapped basic wind speeds are ultimate (strength-level). The nominal (service-level) value is the ultimate pressure scaled by 0.6 — one calculation, two design contexts.

UltimateSTRENGTH LEVEL · LRFD · 1.0W

NominalSERVICE LEVEL · ASD · 0.6W

√0.6 ≈ 0.78NOMINAL SPEED ÷ ULTIMATE SPEED

THE 0.6 RELATIONSHIP

One pressure, two scales

Nominal pressure is exactly 60% of the ultimate pressure. Because pressure scales with the square of speed, the equivalent speed ratio is √0.6 ≈ 0.775.

AT A GLANCE

Ultimate vs nominal, side by side

Ultimate (Strength)

The value read straight off the ASCE 7 wind-speed map since 7-10. Used in LRFD with a 1.0W factor at the strength limit state.

LRFD · 1.0W

Nominal (Service)

The service-level value used in ASD and for deflection checks. Equal to the ultimate pressure × 0.6, i.e. nominal speed ≈ 0.775 V.

ASD · 0.6W

WHICH METHOD USES WHICH

Reference comparison

Aspect	Ultimate	Nominal
Design method	LRFD (strength design)	ASD (allowable stress)
Load factor on W	1.0W	0.6W
Limit state	Strength / failure level	Service level
Map basis (ASCE 7-10+)	Mapped V is ultimate	Derived: pressure × 0.6
Pressure relation	1.00×	0.60× ultimate
Speed relation	V (mapped)	≈ 0.775 V
Typical use	Member strength checks	Drift, DP ratings, ASD combos

WORKED EXAMPLE

From ultimate to nominal

Start with a mapped ultimate speed and walk it down to its nominal, service-level equivalents.

Mapped ultimate speed

V_ult = 150 mph
Read directly from the ASCE 7-22 basic wind-speed map.

STEP 1

Nominal speed

V_nom = V_ult × √0.6
= 150 × 0.775 ≈ 116 mph

STEP 2

Nominal pressure

p_nom = 0.6 × p_ult
Service pressure = 60% of strength pressure.

STEP 3

Key: 150 mph ultimate → about 116 mph nominal. Same wind, two reference levels — never apply the 0.6 factor twice.

WHY IT CHANGED

The ASCE 7-10 map shift

Through ASCE 7-05, the printed wind-speed maps were nominal (service-level), and LRFD applied a 1.6W factor to reach strength.

Starting with ASCE 7-10, the maps were re-cast as ultimate (strength-level) speeds. LRFD now uses 1.0W directly, and ASD recovers the service level with 0.6W.

So when you compare an old 90 mph map to a new 115 mph map, the design intent is unchanged — only the reference level moved from nominal to ultimate.

CALCULATE BOTH AUTOMATICALLY

Get nominal and ultimate in one run

WindLoadCalc.com returns ultimate (LRFD) and nominal (ASD) pressures from a single ASCE 7-22 calculation — no manual 0.6 conversions.

Try Wind Load Calculator ASD ↔ LRFD Conversion

KEEP READING

Nominal vs Ultimate Wind Loads

One pressure, two scales

Ultimate vs nominal, side by side

Ultimate (Strength)

Nominal (Service)

Reference comparison

From ultimate to nominal

Mapped ultimate speed

Nominal speed

Nominal pressure

The ASCE 7-10 map shift

Get nominal and ultimate in one run

Related design-method guides

Nominal Wind Loads

Ultimate Wind Loads

ASD Wind Loads

LRFD Wind Loads

ASD ↔ LRFD Conversion

Wind Load Calculator