How to identify an SMD part
Start with the shape. A rectangle with metal ends is a resistor, capacitor or inductor; a plastic body with two terminals is a diode or a tantalum capacitor, and a band marks the cathode or the positive side; three leads usually mean a transistor, a MOSFET, a double diode or a small regulator; five or six leads, a regulator, a logic gate or a pair of transistors.
Then measure the body without the leads. Packages come in standard sizes, so 2.9 × 1.3 mm is almost certainly a SOT-23 and 2.0 × 1.25 mm an 0805 chip. Finally read the code, every character, and type it as you see it.
Why the codes are so short
A SOT-23 has room for three or four characters, so makers print a short device code instead of the part number: MMBT3904 becomes 1AM, BAV99 becomes A7. Extra characters before or after it are often a date or a factory code: “1AM” from onsemi and “p1A” from Nexperia are both a 3904, while “1Ap” would be a Nexperia BC846A. The same short code can also mean different parts at different makers: the package and the board around it decide.
Resistors, capacitors and inductors
Chip resistors carry their value: 103 is 10 kΩ, 4R7 is 4.7 Ω, 01C is 10 kΩ at 1 %. Ceramic capacitors are almost never marked, so measure them. Tantalum capacitors use the same 3-digit code in picofarads, 107 being 100 µF, and inductors often use it in microhenries.
Resistor colour and SMD code calculator →
Common package sizes
| Package | Also called | Body | Terminals |
|---|---|---|---|
| 0402 | 1005M, 1005 metric | 1 × 0.5 mm | 2 |
| 0603 | 1608M, 1608 metric | 1.6 × 0.8 mm | 2 |
| 0805 | 2012M, 2012 metric | 2 × 1.25 mm | 2 |
| 1206 | 3216M, 3216 metric | 3.2 × 1.6 mm | 2 |
| MiniMELF 0204 | 0204, MMA 0204 (Vishay series) | 3.6 × 1.4 mm | 2 |
| SOD-123 | SOD123 | 2.69 × 1.6 mm | 2 |
| SOD-323 | SC-76, SOD323 | 1.7 × 1.25 mm | 2 |
| SMA | DO-214AC, SMA (J-bend) | 4.3 × 2.6 mm | 2 |
| SMB | DO-214AA, SMB (J-bend) | 4.3 × 3.6 mm | 2 |
| SOT-23 | TO-236AB, SOT-23-3 | 2.9 × 1.3 mm | 3 |
| SOT-23-5 | SC-74A, SOT-25 | 2.9 × 1.6 mm | 5 |
| SOT-323 | SC-70, SC-70-3 | 2 × 1.25 mm | 3 |
| SOT-363 | SC-70-6, SC-88 | 2 × 1.25 mm | 6 |
| SOT-89 | SC-62, TO-243AA | 4.5 × 2.5 mm | 3 |
| SOT-223 | TO-261AA, SC-73 | 6.5 × 3.5 mm | 4 |
| SOIC-8 | SO-8, SOIC-8N (narrow, 150 mil) | 4.9 × 3.9 mm | 8 |
Typical body sizes from JEDEC outlines and manufacturer package drawings. Chips are length × width including the end terminations; leaded packages are the plastic body only.
What is in the database
About 400 marking codes for transistors, MOSFETs, switching and Schottky diodes, rectifiers, zener diodes, TVS and ESD protection, regulators, references, single logic gates and op-amps, each read from the maker’s datasheet, with a link to it. When the same code belongs to several parts, all of them are shown.
Frequently asked questions
What is the SMD code 1AM?
On a SOT-23 it is usually an MMBT3904, a general-purpose NPN transistor: onsemi marks it 1AM followed by a date character. Nexperia marks its own PMBT3904 1A, with a factory character in front; on its own, 1A is also Nexperia’s BC846A.
What is A7 on a 3-pin SMD part?
A BAV99: two switching diodes in series in a SOT-23, often used to protect inputs. Some makers add a date or factory character after A7.
How can I tell a chip resistor from a capacitor?
Resistors are usually black with a printed code, except the smallest (0402 and below), which are often unmarked. Ceramic capacitors are beige, brown or grey and almost never marked. When in doubt, measure the part out of the circuit.
Why do I get several results for one code?
Makers reuse short codes, so the same two characters can be a transistor at one maker and a diode at another. Pick the shape and measure the body: the package usually settles it.
What does the band on an SMD part mean?
On a diode it marks the cathode. On a tantalum capacitor it marks the positive terminal, the opposite of an electrolytic can, where the marked side is negative.