The wing loading calculator above divides weight by wing area and then does the one thing that makes the number useful: it converts it into a speed. Wing loading on its own is just a ratio, quoted variously in newtons per square metre, kilograms per square metre and pounds per square foot depending on whose paper you are reading. What it actually controls is how fast the aircraft has to go before the wing can carry it, how sharply it can turn, and how hard it gets hit by a gust.
Two boundaries before anything else. This is a design and comparison figure, produced from numbers you supply, and certificated aircraft performance comes from the approved flight manual for that aircraft, not from a formula. The published stall speeds in an AFM or POH are flight-test results for a specific configuration, weight and centre of gravity, and they are the only figures that count for operating an aeroplane. Equally, the rules of thumb that circulate in model aviation — target wing loadings in ounces per square foot for a trainer or a pylon racer — are useful shorthand for choosing a design, and they are not airworthiness criteria for anything that carries a person.
What This Wing Loading Calculator Does
It takes a weight in kilograms, pounds or newtons and a planform area in square metres or square feet, and reports the loading in all three conventions at once so you can compare a figure quoted one way against a figure quoted another. Then, given a maximum lift coefficient and an air density, it produces the stall speed that pair implies, both wings-level and in a level banked turn at whatever angle you set.
Arb Digital publishes an adjacent aerodynamics page and the boundary is worth stating. The lift coefficient calculator works the lift equation itself: it takes a coefficient, an area, a speed and a density and returns lift force, dynamic pressure and the mass that lift supports, showing wing loading as a by-product of the force it computed. This page starts from the aircraft rather than from a flight condition — weight over area is the input, not an output — and it exists to compare designs and to invert the lift equation for a speed. The companion thrust to weight ratio calculator covers the other half of the classic design pair.
How to Use It
- Enter the flying weight. Not the empty weight and not the maximum take-off weight unless that is what you are actually at. Wing loading is a condition, not a fixed property of the airframe.
- Enter the planform area. Use the reference wing area from the manufacturer's data if you have it, since that is the area every published coefficient for the aircraft was normalised against.
- Supply a maximum lift coefficient. This is the input the tool cannot guess. It depends on the aerofoil, the planform, the flap setting and the Reynolds number, and getting it wrong scales the stall speed by the square root of the error.
- Set the density. Either from a pressure altitude in the standard atmosphere, or directly if you have a density altitude figure for the day.
- Set a bank angle. The second stall speed shows what a level turn at that angle costs you, which is the number that matters in the circuit.
The Formula: From Loading to Stall Speed
Wing loading is simply W/S, weight divided by reference wing area. Weight is a force, so if you start from a mass in kilograms it becomes m g / S in newtons per square metre. The kilograms-per-square-metre form that light aircraft data sheets use is just m/S, and the pounds-per-square-foot form used in the United States is the same quantity scaled by 0.204816.
The stall speed comes from setting lift equal to weight in the lift equation and solving for velocity. Lift is L = ½ ρ V² S CL, so at the maximum coefficient the wing can reach:
Vstall = √( 2 (W/S) ÷ (ρ CL,max) )
Every term in that expression earns its place. Double the wing loading and the stall speed rises by the square root of two, about 41 per cent. Halve the density by climbing high and the true stall speed rises by the same factor, although the indicated airspeed at the stall barely moves, because the airspeed indicator is measuring dynamic pressure and dynamic pressure is what the wing responds to.
In a level turn the wing must produce more lift than weight, by a factor of n = 1 / cosφ at bank angle φ, and the stall speed scales as Vstall√n. Work the default through: a mass of 1100 kg on 16.2 m² is a loading of 1100 × 9.80665 / 16.2 = 665.88 N/m², or 67.90 kg/m², or 13.91 lb/ft². With CL,max = 1.5 and sea-level density 1.225 kg/m³, Vstall = √(1331.77 / 1.8375) = 26.92 m/s, which is 52.3 knots. At 45 degrees of bank the load factor is 1.414 and the stall speed rises to 32.0 m/s, about 62.2 knots. The lift relation this rests on is set out in NASA's Beginner's Guide page on the lift equation.
What Wing Loading Actually Buys and Costs
Low wing loading means a big wing for the weight. It gives a low stall speed and therefore short field performance, it allows a tight turn radius at a given speed, and it makes the aircraft climb well in weak thermals because the sink rate at any given lift coefficient is lower. That combination is why gliders, bush aircraft and trainers all sit at the low end, roughly 20 to 60 kg/m².
High wing loading means a small wing for the weight, and it buys three things. It buys speed, because a small wing has less area making drag at cruise. It buys ride quality, because a gust changes the angle of attack by roughly the ratio of gust velocity to airspeed, and the resulting change in lift is spread over more weight, so the acceleration the passengers feel is smaller. And it buys structural efficiency, because the wing is smaller and lighter. That is why airliners live at 500 to 750 kg/m² and why a high-performance sailplane deliberately carries water ballast to raise its loading for a fast cross-country day and dumps it before landing.
The cost is entirely at the low-speed end: a higher stall speed, a longer runway, a wider turn, and less margin when things go quiet. Every aircraft design is a decision about where on that trade-off to sit, which is why wing loading and thrust-to-weight ratio are the two numbers plotted against each other in the first sizing diagram of almost every aircraft design textbook.
The Density Trap: Indicated Versus True
This is where the arithmetic misleads people most often. The stall speed this page produces is a true airspeed, because it comes from a real density. Climb to a density altitude of 3000 m and the density falls to about 0.909 kg/m³, which raises the true stall speed by about sixteen per cent for the same aircraft at the same weight.
The airspeed indicator does not show that increase, because it is a differential pressure gauge calibrated for sea-level density, and what it reads is essentially the dynamic pressure. Since the wing also responds to dynamic pressure, the indicated stall speed stays almost constant with altitude. That is enormously convenient in the cockpit and it is also why the true speed, the ground roll and the turn radius all get quietly worse on a hot day at a high field while the number on the dial does not move. The density altitude calculator converts a real field's pressure and temperature into the density altitude this page wants, the air density calculator gives the density directly, and the true airspeed calculator handles the indicated-to-true conversion itself.
Where the Maximum Lift Coefficient Comes From
CL,max is the weakest link in this calculation and the tool deliberately makes you type it in rather than guessing. It is a property of the aerofoil section, modified by the planform, the twist, the surface condition, the Reynolds number and above all the high-lift devices. A clean light-aircraft wing might reach 1.4 to 1.6. The same wing with slotted flaps fully deployed reaches considerably more. A transport wing with slats and multi-element flaps is higher again.
Because the stall speed goes as the inverse square root of the coefficient, an error here is softened but not eliminated: a twenty per cent error in CL,max becomes about a ten per cent error in stall speed, which in a landing calculation is not small. It also degrades in service. Frost, rain, insect contamination on the leading edge and a rough repair all reduce the maximum coefficient without changing anything you can see on the ground, which is one of the reasons published performance figures assume a clean aeroplane. For the forward-flight side of the same wing, the drag force calculator covers what the air does to it in the other direction.
Arb Digital builds free tools like this one because genuinely useful pages earn attention. If you want calculators, tools or technical content built for your own audience, we can help.
Browse All Free Tools Talk to Arb DigitalCommon Mistakes to Avoid
- Treating this stall speed as a performance figure — certificated stall speeds come from the approved flight manual for the specific aircraft, weight and configuration, and are flight-test results rather than formula outputs.
- Using exposed wing area instead of reference planform area — published coefficients are normalised against the reference area including the carry-through, and mixing the two inflates the loading.
- Comparing loadings quoted in different units — kilograms per square metre and pounds per square foot differ by roughly a factor of five, and the newtons-per-square-metre form differs from both again.
- Forgetting the load factor in a turn — at 60 degrees of bank the load factor is 2 and the stall speed is about 41 per cent higher than wings level.
- Applying model-aircraft wing loading conventions to a full-size aircraft — they are a useful design shorthand for models and are not airworthiness criteria.
Related Free Tools From Arb Digital
For the lift equation itself rather than the loading, use the lift coefficient calculator, and for the other half of the sizing pair the thrust to weight ratio calculator. Density is handled by the air density calculator and the density altitude calculator, and the true airspeed calculator converts between indicated and true. The drag force calculator covers the resistance side, while the crosswind component calculator and ground speed calculator deal with the wind. The weight converter reconciles units between data sheets. Everything Arb Digital publishes is indexed on the free online tools hub. The aerodynamic theory underneath is developed in MIT OpenCourseWare's 16.100 Aerodynamics, and the operational treatment is in the FAA's Pilot's Handbook of Aeronautical Knowledge.
Frequently Asked Questions
It is the aircraft's weight divided by its reference wing planform area, quoted as newtons per square metre, kilograms per square metre or pounds per square foot depending on the source. It is a condition rather than a fixed property, because it changes with fuel burn and payload, and it is the single figure that most directly controls stall speed, turn radius and ride quality in turbulence.
No. It is an idealised aerodynamic result from the numbers you entered, assuming a rigid wing at its maximum lift coefficient in steady flight. Certificated stall speeds are flight-test results published in the approved flight manual or pilot operating handbook for a specific aircraft at a specific weight, configuration and centre of gravity, and those are the only figures that count for operating an aeroplane.
Because a gust changes the wing's angle of attack by roughly the ratio of the gust velocity to the airspeed, and the lift increment that produces is spread across more weight. The same disturbance therefore produces a smaller acceleration. That is one of the reasons airliners cruise at wing loadings several times those of a light aircraft, and why a light aircraft feels every bump.
The true airspeed at the stall rises as density falls, by the inverse square root of the density ratio, so a climb to a density altitude of 3000 metres raises it by roughly sixteen per cent. The indicated airspeed at the stall barely changes, because the airspeed indicator reads dynamic pressure and the wing responds to dynamic pressure. The consequences of the higher true speed still show up in ground roll and turn radius.
In a level turn the wing must carry a load factor of one divided by the cosine of the bank angle, and the stall speed rises as the square root of that load factor. Thirty degrees of bank gives a load factor of 1.15 and about seven per cent more stall speed; forty-five degrees gives 1.41 and about nineteen per cent; sixty degrees gives 2.0 and about forty-one per cent.
One that belongs to your actual wing and flap setting, taken from the aerofoil data, wind tunnel results or the manufacturer's figures. This tool cannot infer it, because it depends on the section, the planform, the twist, the Reynolds number and the high-lift devices. Because stall speed varies as the inverse square root of the coefficient, a twenty per cent error in it becomes roughly a ten per cent error in speed.
That page works the lift equation forwards: given a coefficient, an area, a speed and a density it returns lift force and dynamic pressure, and shows wing loading as a by-product of the force it computed. This page starts from the airframe instead, taking weight over area as the input, and inverts the lift equation to find the speed at which the wing can just carry that loading. One describes a flight condition, the other describes a design.
They are useful shorthand within model aviation, where target loadings in ounces per square foot separate a docile trainer from a fast pylon design, and the underlying physics is the same. They are not airworthiness criteria. Anything that carries a person is governed by certification standards and by the approved flight manual for that type, and no rule of thumb substitutes for either.
This page produces a design and comparison figure from the values you enter. It is not an approved planning tool and it does not replace the aircraft flight manual or pilot operating handbook, which govern the performance of any certificated aircraft.
