Stall Speed Calculator - Calculator Academy

Estimate aircraft stall true airspeed (TAS) from weight, wing area, aircraft-specific CLmax, air density and a positive load factor. The calculator also shows equivalent airspeed (EAS); it does not calculate an atmosphere from altitude or torque-converter RPM.

Estimate true airspeed (TAS) for the stated positive load factor. Default load is 1g.

Educational aerodynamic estimate. Enter aircraft-specific CLmax and local density. Use the aircraft’s AFM/POH for operating speeds.

Aircraft weight / mass

Kilograms are mass converted to weight using standard gravity.

Wing planform area

Maximum lift coefficient (CLmax)

Use data for the actual aircraft and configuration.

Air density

Default: standard sea-level density, 1.225 kg/m³. Replace it for actual conditions.

Positive load factor (g)

Default 1g. Bank angle alone does not determine load factor in general flight.

Illustrative CLmax values

CLmax example

Illustrative numbers only; these do not identify a wing or flap configuration.

Stall Speed Formula

For the specified configuration and positive load factor, this model estimates the true airspeed at which the required lift reaches the maximum lift associated with CLmax. The stall itself is caused by angle of attack, not by a single fixed speed, which is why stall speed changes with weight, flap setting, bank angle, icing, and air density.

Vₛ = \sqrt((2L) / (C L,max ρ S))

In steady 1g level flight, required lift is usually equal to aircraft weight, so the same relationship is often written as:

Vₛ = \sqrt((2W) / (C L,max ρ S))

Variable	Meaning	Typical Notes
V_s	Stall speed	This density-based equation gives TAS; EAS is also shown. IAS needs aircraft-specific corrections.
L	Required lift force	In straight-and-level 1g flight, this is typically equal to weight
W	Aircraft weight	Use force units such as N or lbf
C_L,max	Maximum lift coefficient	Use the value for the actual configuration at stall
ρ	Air density	Changes with altitude, temperature, and pressure
S	Wing planform area	Use the lifting surface area assumed by the aircraft data

Rearranging the Equation

The widget solves for TAS from the entered conditions. The following algebraic rearrangements explain the underlying lift relationship; inverse solving is not a widget mode. With load factor n, required lift is L = nW:

L = (Vₛ² C L,max ρ S) / (2)

C L,max = (2L) / (Vₛ² ρ S)

ρ = (2L) / (Vₛ² C L,max S)

S = (2L) / (Vₛ² C L,max ρ)

How to Use the Stall Speed Calculator

Enter aircraft weight or mass. Select N or lbf for force, or kg for mass converted using standard gravity. Required lift is n × weight; the default positive load factor is 1g.
Enter the maximum lift coefficient. Use C_L,max for the exact configuration being analyzed, such as clean, takeoff flap, or landing flap.
Enter air density. Density falls as altitude increases and also changes with temperature and pressure.
Enter wing area. Use wing planform area, keeping units consistent with the rest of the calculation.
Set the positive load factor and select Calculate. The result is an ideal TAS estimate for the entered conditions. Example CLmax choices are illustrative only; use aircraft-specific configuration data. Consult the AFM/POH for operating speeds.

Unit tip: Keep the entire equation in one unit system. For hand calculations, use N, kg/m³ and m², or lbf, slugs/ft³ and ft². The widget converts each selected input unit internally. The lbf option is pounds-force; the kg option is mass multiplied by standard gravity, 9.80665 m/s². Changing an input unit converts an entered quantity.

What Changes Stall Speed?

Change	Effect on Stall Speed	Why It Happens
Higher weight	Increases	More lift is required, so the wing must operate at a higher dynamic pressure before reaching C_L,max.
Higher C_L,max	Decreases	A wing that can make more lift before stalling can fly slower before reaching the critical angle of attack.
Lower air density	Raises stall TAS	Thin air requires more true speed to create the same lift.
Larger wing area	Decreases	More lifting surface reduces the speed needed to support the aircraft.
Higher load factor	Increases	Turning or pulling G increases required lift above simple 1g weight support.
Ice, contamination, or damage	Usually increases	These conditions often reduce attainable C_L,max and disturb airflow over the wing.

Useful Stall Speed Relationships

Two of the most important real-world changes are weight and load factor.

V s,2 = V s,1 \sqrt((W₂) / (W₁))

This means stall speed changes with the square root of weight. A 21% increase in weight produces about a 10% increase in stall speed.

V s,n = V s,1g \sqrt(n)

For a positive load factor, the ideal stall speed scales with √n; n above 1 raises it above the 1g value. Only in a coordinated, constant-altitude turn does bank angle determine load factor through:

n = (1) / (cos φ)

At a 60° bank, the load factor is 2, so stall speed becomes about 1.414 times the 1g stall speed.

Altitude, IAS, and TAS

For the same aircraft weight, configuration and load factor, stall equivalent airspeed is constant in this fixed-CLmax model. EAS = TAS × √(ρ / 1.225), with density in kg/m³. At low speed, IAS may approximate EAS when instrument, position and compressibility effects are negligible. Density alone does not determine an aircraft-specific IAS reading. True airspeed at the stall increases as density decreases.

V s,TAS \propto (1) / (\sqrt(ρ))

That is why an aircraft may stall at roughly the same indicated airspeed at sea level and at altitude, while the actual speed through the air is higher at altitude.

Example Calculation

If the required lift is 9,800 N, the maximum lift coefficient is 1.5, the air density is 1.225 kg/m³, and the wing area is 16.2 m², then:

Vₛ = \sqrt((2(9800)) / (1.5(1.225)(16.2))) \approx 25.66 m / s

This corresponds to a stall speed of about 49.9 knots.

Practical Notes

Use C_L,max for the exact aircraft configuration. Flaps, slats, and other high-lift devices can change stall speed significantly.
The equation is most useful as a clean aerodynamic estimate. Published aircraft handbook values should always take priority for actual operation.
Wing contamination, turbulence, and maneuvering can make the effective margin above stall smaller than the simple 1g calculation suggests.
A stall can occur at any airspeed if the wing exceeds its critical angle of attack.

FAQ

Does higher weight increase stall speed?

Yes. Heavier aircraft need more lift, so the wing must fly at a higher airspeed before reaching the maximum usable lift coefficient.

Do flaps reduce stall speed?

Usually yes. Flaps generally increase C_L,max, which lets the wing support the aircraft at a lower airspeed before stalling.

Does stall speed increase with altitude?

It increases in true airspeed, but for the same weight and configuration it remains nearly the same in indicated airspeed.

Can an airplane stall above the published stall speed?

Yes. Published stall speeds are typically based on specific configurations and load factors. Banking, pulling G, or abrupt control inputs can cause a stall at a much higher airspeed.

Correct stall-speed relationship: V_s,TAS = √[2L / (ρ × S × C_L,max)] = √[2nW / (ρ × S × C_L,max)]. Here L is required lift, W is aircraft weight, n is positive load factor, ρ is air density and S is wing planform area. Use consistent force, density and area units.