If you have taken a short-haul flight anywhere in the world in the last thirty years, there is a very good chance you were on either a Boeing 737 or an Airbus A320. Between the two families, these aircraft account for something like sixty percent of the global commercial fleet. They serve the same market, carry roughly the same number of passengers, and fly the same kinds of routes. From a distance, they look close enough that most passengers cannot tell them apart.

They are not the same aircraft. They were designed twenty years apart, by two competing manufacturers, using fundamentally different design philosophies. Once you know what to look for, you can identify which one you are boarding from the jet bridge. You can even tell from a plane in the sky if you can get a clear view of it. The differences are visible, and they are a window into how modern commercial aviation evolved.

The engines give them away every time

The single most reliable way to tell a 737 from an A320 is the shape of the engine nacelle, meaning the casing that wraps around the engine itself. Look at the front of an engine on an Airbus A320. It is a perfect circle. Now look at the front of an engine on a Boeing 737. It is flattened on the bottom. The top half of the nacelle is circular, the bottom is squared off, and the whole thing looks a little like a D on its side.

This is not an aesthetic choice. It is a consequence of how old the 737 design is. The original Boeing 737 entered service in 1968. At that time, jet engines were narrower than they are today, and the airport infrastructure used to service them was less sophisticated. Boeing designed the 737 with very short landing gear so that ground crews could load baggage by hand, without needing a dedicated conveyor belt. The aircraft sits low to the ground.

When engine technology evolved in the 1980s, engines became wider because bigger fans move more air with less noise and better fuel efficiency. Airbus designed the A320 around those newer engines from the start, with taller landing gear that gave the nacelles plenty of ground clearance. Boeing had to fit the same generation of engines onto an aircraft that was already sitting low. The solution was to flatten the bottom of the nacelle so the engine could clear the runway during takeoff. Every 737 built since the 1980s has that flattened nacelle, and it has become the single most distinctive visual element of the type.

On the 737 MAX, released in 2017, the effect is even more pronounced. The MAX uses an even larger engine, which required moving the engine forward and up to maintain ground clearance. The nacelle looks stubby and slightly misshapen compared to the sleek, round engine of an A320neo.

The cockpit windows

The second most reliable identifier is the shape of the cockpit windows. On a 737, the two main windshield panels slope down to a point at the nose, and there are additional eyebrow-shaped windows above the main windshield on older models. The overall geometry is angular, with visible creases where the different glass panels meet.

On the A320, the cockpit windows are almost flat and nearly rectangular. The main windshield is a clean pair of near-vertical panels with a slightly rounded outer edge. There are no eyebrow windows. The profile of the nose is smoother and rounder than the 737, less like a speedboat and more like a whale.

Some older 737s, particularly 737 Classic and earlier 737 Next Generation variants, still have the eyebrow windows. Boeing eliminated them in later builds because they were mostly there as holdovers from a time when pilots used celestial navigation and needed an upward view. Modern navigation does not require them, and the windows added weight and complexity to the airframe. If you are looking at a 737 built before 2005 or so, you will probably see the small trapezoidal window above the main windshield. If it is a newer build, the space where the eyebrow window used to be is covered by a metal panel, visible as a slightly different color from the surrounding fuselage.

The nose shape

The overall shape of the nose follows from the cockpit design. The 737 has a more pointed nose that tapers sharply. The A320 has a blunter, rounder nose that bulges out slightly. From the side, the A320 looks like it has a higher forehead. From head-on, the 737 looks narrower and more aggressive.

This difference is partly aerodynamic and partly historical. The 737 design inherited many elements from the 707, which was optimized for high-speed long-haul flight in the 1950s. The A320 was designed later, with more modern computational fluid dynamics tools and a different set of aerodynamic priorities. The rounder A320 nose is not worse aerodynamically, it is just a different solution to the same set of constraints.

The tail and the APU

At the back of the aircraft, the differences are more subtle but still visible. The 737's tail has a distinctive rudder shape with a clear hinge line. The A320's rudder is slightly different in proportion. More tellingly, the auxiliary power unit exhaust, which is the small vent at the very rear of the tail cone, is shaped and positioned differently on the two aircraft. On the 737, the APU exhaust is a rounded oval opening. On the A320, it is a more rectangular slot with distinctive fins.

These are not features most passengers notice, but they are dead giveaways for aviation enthusiasts looking at a plane from the ground.

The wingtips

Wingtip design has become one of the most visible differentiators on modern aircraft, because it is the area where both manufacturers have been innovating most aggressively.

On the Boeing 737 Next Generation, the standard wingtip is a blended winglet, which is a single upward-curved extension that looks like a fin. Some operators have upgraded their 737 NG fleets with split scimitar winglets, which add a small downward-facing blade to the existing winglet. The 737 MAX was designed from the start with the split scimitar design, which looks like a bird wingtip.

On the Airbus A320, older aircraft had wingtip fences, which are small upward-and-downward fins that look like miniature rabbit ears. The A320neo, introduced in 2016, comes standard with sharklets, which are upward-only blades similar in concept to the 737 NG's blended winglets but with a different curve profile. The A320neo's sharklets curve more smoothly and extend further upward.

If you see an aircraft with rabbit-ear wingtip fences, it is an older A320. If you see smoothly curved upward blades with no downward component, it is a newer A320neo with sharklets. If you see a winglet with both an up and a down component, it is either a 737 MAX with split scimitars, or a 737 NG that has been retrofitted.

The landing gear tells the age of the design

The most under-appreciated spot-the-difference test is the landing gear. Boeing 737s have short landing gear, which is why the fuselage sits low to the tarmac. If you watch a 737 land, you will see it settle noticeably close to the ground once its wheels are down. A320s sit taller. Their landing gear is longer, and there is more visible space between the underside of the fuselage and the runway.

Stand at a gate window looking down the line of parked aircraft at a major airport and you can often identify the 737s by how low they sit. The nose gear in particular is much shorter on the 737, and the aircraft often looks like it is leaning forward slightly at rest. The A320 looks more level.

This is all downstream of the same original design choice. Short gear meant easier baggage handling in 1968. It also meant that every subsequent generation of the 737, for sixty years now, has had to work around the constraint of low ground clearance. The A320 did not inherit that constraint, and it shows.

The family context: why there are so many variants

Neither the 737 nor the A320 is a single aircraft. Both are families of variants that have evolved over decades.

The 737 family, in rough historical order, includes the original 737-100 and 737-200, the 737 Classic (300, 400, 500), the 737 Next Generation (600, 700, 800, 900, 900ER), and the 737 MAX (7, 8, 9, 10). The MAX is the current-production variant. When you board a 737 operated by a major airline today, it is almost certainly a 737 NG (usually the 737-800) or a 737 MAX (usually the MAX 8). The older Classics are mostly retired in developed markets but still fly in cargo and some regional operations.

The A320 family includes the original A318 (small), A319 (mid-small), A320 (baseline), and A321 (stretched), in the original ceo (current engine option) configuration. Airbus then introduced the neo (new engine option) family, which covers the A319neo, A320neo, and A321neo, with additional long-range variants like the A321LR and A321XLR. The neo family uses newer engines and updated aerodynamics for fuel efficiency.

The two families have been in direct commercial competition for over thirty years. Airbus has been outselling Boeing in the single-aisle market for about a decade, partly due to the commercial fallout of the 737 MAX grounding in 2019-2020, and partly due to the A321neo's strong position in the medium-haul single-aisle segment where Boeing has struggled to offer a direct competitor. Both families have delivered over ten thousand aircraft. Together, they define what short-haul commercial aviation looks like.

What it looks like from your window seat

If you have a window seat and the aircraft type is not announced clearly, you can still often tell which family you are on.

Look at the engine. If you can see the front face of it, is it round, or is it flattened at the bottom? Round means A320 family. Flattened means 737.

Look at the wingtip. Is there a downward component to the winglet? If yes, you are on a 737. If it is only upward, you could be on either (sharklets on A320neo or blended on older 737 NG, although the curvature profile is different).

Listen during taxi. The APU on a 737 has a slightly different sound profile from the A320, but unless you are an enthusiast this is not a useful identifier.

Once in flight, if you look down at the wing, the 737's wing has a sharper leading-edge sweep and fewer visible fairings compared to the A320's wing, which tends to be smoother and has a slightly different profile. But this is subtle and hard to judge from a window seat.

The most reliable in-flight test remains the engine shape, which you can sometimes glimpse as the aircraft taxis past another gate, or when you are boarding from a jet bridge that gives you a side view of the parked aircraft.

Why this matters

Most passengers do not care which family they are on, and there is no particularly good reason they should. Both aircraft are safe, well-understood, and operated by flight crews who train extensively on their specific type. The flight experience is dominated by the airline's seating configuration, the route length, and the specific crew on that day, not by whether the aircraft was designed in Toulouse or Renton.

But the 737 and the A320 are also two of the most consequential industrial products of the twentieth century, and they represent two different philosophies of how to build an airliner. The 737 is a continuous evolution of a 1960s design, preserving certain original characteristics (like the low-slung fuselage and the narrow cabin) even as the manufacturer adapts them to new engines and new technology. The A320 was a clean-sheet design from the 1980s, built from the start around fly-by-wire flight controls and a different cockpit philosophy. The two aircraft compete head to head on almost every short-haul route in the world, and they have done so for more than three decades.

Knowing which one you are on is a small thing. But once you can tell them apart, every airport looks a little different. The shapes start to mean something, and the history of how we got here becomes visible in the machines themselves.