What is the difference between through-hole (PTH) and surface-mount (SMD) resistors?
Through-hole resistors have wire leads that go through holes, fit into a breadboard and use colour bands; surface-mount resistors are tiny blocks soldered onto pads on the surface of a PCB and use a printed number code.
| Through-hole (PTH) | Surface-mount (SMD) | |
|---|---|---|
| Mounting | Leads pushed through holes and soldered on the other side, or into a breadboard | Soldered onto pads on top of the PCB |
| Size | Several millimetres, easy to handle | Down to fractions of a millimetre |
| Value marking | Colour bands | Printed numeric code, e.g. 472 = 47 × 10² = 4.7 kΩ |
| Where you meet it | Prototyping, breadboards, hobby kits | Almost every mass-produced board, including the ESP32 dev board |
The split mirrors the IoT development path. You prototype with through-hole parts on a breadboard because you can plug them in and swap them. The product is then made with SMD parts because they are smaller, cheaper and can be placed by machine.
Resistors also come as resistor packs (several in one package) and variable resistors such as the potentiometer, whose resistance changes when you turn the knob.
Tip: the SMD code uses the same idea as the colour bands: two digits then the number of zeros.
Go deeper:
Wikipedia — Surface-mount technology — why SMD replaced through-hole in manufacturing, and its package sizes.