ISRO PSLV-C37 onboard camera showing 104 satellite separation

A CubeSat (U-class spacecraft) is a type of miniaturized satellite for space research that is made up of multiples of 10×10×11.35 cm cubic units. CubeSats have a mass of no more than 1.33 kilograms per unit, and often use commercial off-the-shelf (COTS) components for their electronics and structure.

The term "CubeSat" was coined to denote nanosatellites that adhere to the standards described in the CubeSat design specification.

Source: https://en.wikipedia.org/wiki/CubeSat

It's hard to find photos that give any size reference, but a 3U cubesat is about 3 liters of volume.

In this launch, there were "3U", "2U" and "1U" sized CubeSats[1]. 1U CubeSat is a 10x10x10 cm3 cube[2], "2U" is 20x10x10 cuboid and "3U" is 30x10x10 cuboid.

[1] https://news.ycombinator.com/item?id=13650114

[2] https://en.wikipedia.org/wiki/CubeSat

In the case of the Planet satellites, they will be spread out using differential drag over the next few months.

https://arxiv.org/pdf/1509.03270.pdf