How Big is a Drop of Water?

Have you ever wondered how big a drop of water is? While it might sound like it could be any size or volume, a “drop” is actually a semi-standardized form of measurement that refers to the amount of liquid dispensed from a dropper or drip chamber.

A water drop will typically measure around 0.5 to 4 millimeters in size, though the size typically falls within the 2 to 2.5-millimeter range. In terms of volume, a single drop of water will measure roughly 0.05 milliliters.

So, what constitutes a drop of water, what factors come into play in determining the size of the drop, and how many drops of water will it take to fill a 1-liter vessel? Find out in the following sections.

What Is a Drop of Water?

A drop of water is defined as a small amount of liquid that is almost completely bound by free surfaces. Drops or droplets can be dispensed from liquid drippers, drops, or fall from the sky during rainfall.

Size and Volume of a Drop of Water

The physical size of a drop of water will vary, depending on what vessel it is dispensed from. On average, a raindrop will measure 0.5 to 4 millimeters in diameter, with most raindrops measuring 2 to 2.5 millimeters wide.

Before the unit “minim” was adopted in the 19th century, a drop of water was presumed to be 1/60 of a fluid dram, 1/480 of a fluid ounce, or roughly 61.6 μL. When the apothecaries’ system was adapted, a drop of water was rounded up to 0.05 milliliters, so 20 drops of water would equal precisely 1 milliliter.

What Affects the Size of a Drop of Water?

While a drop is considered to be 1/20 of a milliliter, the size and volume of a single droplet of water will depend on the opening of the liquid dispenser. However, a drop will usually have a maximum diameter of 4 millimeters, even when pouring out of a half-inch PVC pipe.

Other variables that could affect the size of a drop include the viscosity and density of the liquid, as well as surface tension (the tension produced by a surface that attracts particles).

In technical terms, the size of a droplet will be affected by fluid inertia and surface tension—two important parts in nozzle geometry, a field that aims to measure the liquid flow rate while minimizing pressure drop.

How Many Water Drops to Fill a Container?

Since a single drop of water takes up 0.05 milliliters in volume, we can easily calculate how many drops it would take to fill a container of any size, which you can find in the following table.