To answer the question from the title:
Not all PCI cards are the same size. Some are half height. Some are regular (full height).
Some PCI card only use a 32 bit slot (mostly in PC desktops), while others use the 64 bit interface. The latter are usually larger, partially due to the larger connector size.
This picture gives a nice indication of slot size of 32 bit 64bit PCI, though actual card sizes can ofc be larger. (Picture source: Wikipedia)
Now you mentioned laptops. While some laptops accept regular PCI cards in their docking-stations I assume you might means either. MiniPCI, MinePCIe, PCMCIA, PCCARD or express card.
The first two look like this: (Picture source: Wikipedia)
I have installed a few of these cards and their sizes does vary by at least a factor 2.
As for the remaining 3:
PCMCIA is more or less a creditcard size ISA bus.
PCCARD is more or less a creditcard size PCI bus.
Both cards are equally large by design, though some of them add bulky connectors while other use plug in cables.
Here is an example of one with an external antenna (and thus larger than normal).
Their height on the other hand can vary. Almost all cards are single height, as are most slows. Though there are a few cards which need more room for electronics or who build their plugs directly into the card.
The next generation (From PCMCIA, to PCCARD (16 bit), PCCARD (32bit) is cardbus).
As you can see it comes in two different widths, with cardbus 34 fitting in all slots, and cardbus 54 fitting on extra wide slots.