Raindrop Size, Shape and Speed: What Raindrops Really Look Like

Ask someone to draw a raindrop and they'll probably make the familiar teardrop shape — rounded at the bottom and pointed at the top. Real raindrops look nothing like that. As they fall through the atmosphere, their shape and speed are determined by a combination of gravity, air resistance and surface tension.

What Shape Is a Raindrop?

Very small raindrops are almost perfectly round because surface tension pulls the water molecules together into a sphere. As a drop gets larger and falls faster, however, air resistance pushes against its underside. The bottom begins to flatten while the top remains rounded.

A medium-sized raindrop actually looks more like a hamburger bun than a teardrop. Larger drops become even flatter and may develop a depression underneath. Eventually, the forces acting on a very large drop become too strong for surface tension to hold it together, and the drop breaks apart.

How Big Are Raindrops?

Raindrops vary considerably in size. Tiny drizzle droplets may be less than 0.5 millimeter across, while ordinary raindrops are often around 1–2 millimeters in diameter. Heavy rain and thunderstorms can produce drops several millimeters across.

There is a practical upper limit, though. Raindrops generally can't remain intact once they reach roughly 6 millimeters — about ¼ inch — in diameter. At that size, airflow distorts them so much that they tend to break into smaller drops. That's why you don't see golf-ball-sized raindrops falling from the sky: liquid water simply can't hold itself together at that size while falling through the atmosphere.

How Fast Does a Raindrop Fall?

A raindrop doesn't continue accelerating all the way to the ground. Gravity pulls it downward while air resistance pushes against it, and eventually those forces balance. At that point the drop has reached terminal velocity, the speed at which it will continue falling.

That speed depends largely on the size of the drop. Tiny droplets may fall at only a few miles per hour, while a typical raindrop can fall around 15–20 mph. The largest stable raindrops can approach roughly 20–25 mph, which helps explain why the big drops in a summer thunderstorm can feel surprisingly forceful when they hit your skin.

Speed is only part of the trip. Depending on the height of the cloud and the conditions below it, a raindrop may fall thousands of feet and change considerably before it ever reaches the ground.

Why Don't Raindrops Keep Getting Bigger?

Inside a cloud, tiny water droplets can collide and combine with one another in a process called coalescence. As this happens repeatedly, some drops grow large enough to begin falling toward the ground. You can read more about that process in How Rain Forms: From Water Vapor to Raindrops.

But growing larger also makes a falling drop less stable. Increasing air resistance flattens and distorts it until surface tension can no longer keep the water together. The drop then breaks into smaller droplets. There is a constant competition between surface tension trying to hold the drop together and aerodynamic forces trying to pull it apart — and at around 6 millimeters, the air usually wins.

Why Do Thunderstorm Raindrops Seem So Big?

If you've ever watched a summer thunderstorm begin with enormous, widely spaced drops, you're not imagining the difference. Strong storms can contain powerful updrafts that keep water droplets suspended longer, giving them more opportunities to collide and grow before they finally become heavy enough to fall.

Those large thunderstorm drops can be noticeably bigger than the droplets in a gentle rain, but they are still subject to the same physical limits. If they become too large and unstable on the way down, they'll break apart before reaching the ground.

Large drops are also only one characteristic of a heavy downpour. Rainfall intensity measures how quickly rain is actually falling, regardless of the size of the individual drops.

From Cloud to Ground

The familiar pointed raindrop is a useful symbol, but it's not a shape you'll find falling from a cloud. Small drops are nearly spherical, larger ones flatten as they fall, and drops that become too large eventually break apart.

Every falling raindrop is a small demonstration of competing physical forces: gravity pulling it toward Earth, air resistance pushing against it and surface tension trying to hold it together. Its size determines not only its shape, but also how quickly it makes the journey from cloud to ground.