Resistor package sizes split into three families: rectangular chip (SMD) resistors, cylindrical MELF resistors, and heatsink-mounted power resistors. Chip sizes run from 01005 to 2512 and handle roughly 0.03 W to a few watts. MELF trades placement ease for lower temperature drift and stronger pulse handling. Power packages move tens to hundreds of watts, but only on a heatsink. This guide gives the dimensions, power, and voltage limits you actually design against.
Key takeaways
- Chip codes are dimensions: imperial 0603 means 0.060 in × 0.030 in, or 1.6 mm × 0.8 mm (metric 1608).
- Watch the code system: metric 0603 (0.6 × 0.3 mm) is the same part as imperial 0201 — a real ordering trap.
- Standard thick-film chip power runs 0.063 W (0402) to 0.25 W (1206) at 70 °C, per Vishay CRCW…C e3, and each size also carries a voltage ceiling: 0402 = 50 V, 1206 = 200 V.
- MELF (0102 / 0204 / 0207) gives 25–50 ppm/K TCR and higher pulse strength than a same-size flat chip, at the cost of pick-and-place roll.
- A power resistor’s nameplate wattage is a heatsinked number. In free air, the same TO-220 or aluminum-housed part handles a fraction of it.
The three resistor package families at a glance
Before the size charts, it helps to place the three families side by side. Each solves a different problem: density, stability, or heat.
[IMAGE 1: three resistors side by side — a 0603 chip, a MiniMELF cylinder, and a TO-220 power resistor on a heatsink | alt: “resistor package sizes compared: chip, MELF and power resistor families”]
| Family | Construction | Size range | Power range | Where it fits |
| Chip (SMD) | Rectangular thick/thin film | 01005 to 2512 | ~0.03 W to ~2 W | General-purpose, high-density digital and analog boards |
| MELF | Cylindrical film, metal end caps | 0102 / 0204 / 0207 | ~0.2 W to ~1 W | Precision, low-drift, pulse-exposed circuits |
| Power | Molded / aluminum-housed, leaded or bolt-down | TO-220 to SOT-227 and larger | ~1 W to 2 kW | Braking, current sensing, dummy loads, supply dissipation |
The rest of this guide takes them in order, because most designs start with a chip resistor and only move to MELF or a power package when drift or heat forces the change.
Chip (SMD) resistor sizes
The standard SMD chip sizes are 01005, 0201, 0402, 0603, 0805, 1206, 1210, 2010, and 2512. The four-digit code is the body’s length and width: imperial in hundredths of an inch, metric in tenths of a millimeter. So imperial 0603 is 0.060 in × 0.030 in, which is 1.6 mm × 0.8 mm, and the same body is metric 1608.
[IMAGE 2: labeled top-down chip resistor with length and width callouts and the imperial/metric code | alt: “SMD chip resistor size code showing length and width in imperial and metric”]
The table below lists the common packages with nominal body dimensions, typical power at 70 °C, and the maximum working voltage. Dimensions are per the Vishay D/CRCW datasheet (doc 20008); power and voltage are per the Vishay CRCW…C e3 and CRCW…BC e3 datasheets. Always confirm against the specific part.
| Imperial | Metric | L × W (mm) | L × W (in) | Typ. power @70 °C | Max working V |
| 01005 | 0402 | 0.4 × 0.2 | 0.016 × 0.008 | 0.031 W | 15 V |
| 0201 | 0603 | 0.6 × 0.3 | 0.024 × 0.012 | 0.05 W | 25–30 V |
| 0402 | 1005 | 1.0 × 0.5 | 0.040 × 0.020 | 0.063 W | 50 V |
| 0603 | 1608 | 1.6 × 0.8 | 0.060 × 0.030 | 0.10 W | 75 V |
| 0805 | 2012 | 2.0 × 1.25 | 0.079 × 0.049 | 0.125 W | 150 V |
| 1206 | 3216 | 3.2 × 1.6 | 0.126 × 0.063 | 0.25 W | 200 V |
| 1210 | 3225 | 3.2 × 2.5 | 0.126 × 0.098 | 0.5 W | 200 V |
| 2010 | 5025 | 5.0 × 2.5 | 0.197 × 0.098 | 0.75 W | 400 V |
| 2512 | 6332 | 6.3 × 3.2 | 0.248 × 0.126 | 1 W | 500 V |
These sizes are not arbitrary. Vishay references EIA-575 and CECC 40401-802 for the code and outline (per D/CRCW datasheet doc 20008), and the resistance values in each package follow the IEC 60063 E-series sets — E24 for 5 % parts, E96 for 1 %. That standardization is why an 0603 from one vendor drops onto another vendor’s 0603 land pattern.
For hand assembly, 0805 and 1206 are the forgiving sizes. 0603 is workable with flux, fine tweezers, and good light. 0402 is possible but far less forgiving, and 0201 and 01005 are reflow-first parts that fight manual rework.
Imperial vs metric codes: the 0603 trap
Here is where orders go wrong. Imperial 0603 and metric 0603 are not the same part. Imperial 0603 is 1.6 mm × 0.8 mm. Metric 0603 is 0.6 mm × 0.3 mm — which is imperial 0201. Reading one code as the other swaps a mid-size chip for a near-invisible one.
The habit that prevents it: most of the industry uses imperial codes but talks in millimeters during layout. Label every line in your BOM with both codes, like “0603 / 1608,” and confirm the system with the supplier before you order. DigiKey notes these two-terminal SMD outlines are maintained as standard shapes, so once you fix the code system, the footprint follows.
[INTERNAL LINK: reading SMD resistor codes -> 3-digit / 4-digit / EIA-96 marking]
Power and voltage limits by chip size
A chip resistor’s rating is not one number. It is a power at a reference temperature *and* a voltage ceiling, and both matter.
The power figures above are rated at 70 °C ambient. Above that, the part derates linearly to zero at the maximum film temperature, which Vishay specifies as 155 °C for standard and anti-surge thick-film chips (per RCS e3 datasheet doc 20065). That derating is easy to forget and it bites in hot enclosures.
Worked example. Take an 0805 rated 0.125 W at 70 °C. In a 105 °C enclosure, the allowable dissipation is:
P = 0.125 W × (155 – 105) / (155 – 70) = 0.125 × 50 / 85 ≈ 0.074 W
So a part you think of as “1/8 watt” is really about 74 mW where it lives. Size for the ambient, not the datasheet headline.
The voltage ceiling is the second limit. Past roughly 200 V, package length — not power — sets the part, because a longer body holds off more voltage across its ends. That is why high-voltage dividers use 1206, 2010, or 2512 even at low power.
When a standard chip cannot take the pulse or power, Vishay offers pulse-proof and anti-surge variants in the same footprints — CRCW-HP e3 (higher rated dissipation, e.g., a 2512 reaching 2–3 W) and RCS e3 (anti-surge). Reaching for a bigger footprint is not the only lever; a tougher part in the same size can be.
[INTERNAL LINK: resistor power derating & thermal design -> thermal design for passives]
MELF resistor sizes
MELF stands for metal electrode leadless face: a cylindrical ceramic body with a deposited film and metal end caps. There are three sizes — MicroMELF (0102), MiniMELF (0204), and MELF (0207).
The cylinder is the point. It gives about three times the film area of a flat chip of similar footprint, so heat spreads and the temperature coefficient drops. Thin-film MELF runs 25–50 ppm/K, against >200 ppm/K for typical thick-film chips (per EEPower’s resistor guide), and its pulse capability is markedly higher than a same-size flat chip.
| Case (metric) | Common name | Dia × L (mm) | Power @70 °C | Max working V | TCR (thin film) |
| 0102 | MicroMELF | 1.1 × 2.2 | 0.2–0.3 W | 150 V | 25–50 ppm/K |
| 0204 | MiniMELF | 1.5 × 3.6 | 0.25–0.4 W | 200 V | 25–50 ppm/K |
| 0207 | MELF | 2.2 × 5.8 | 0.4–1.0 W | 300 V | 25–50 ppm/K |
Vishay’s MELF datasheet (doc 28802) anchors the endpoints: operating voltage from 150 V (0102) up to 300 V (0207), rated power from 0.3 W (0102) up to 1 W (0207) at 70 °C, and a maximum film temperature of 155 °C, with high-temperature versions rated to +175 °C. Vishay also maps the cylindrical 0102 / 0204 / 0207 to flat-chip 0805 / 1206 / 2512 in power and application terms — useful when swapping between the two.
For the same part, Vishay specifies power in tiers. A 0204 in the MMA HT line is rated 0.25 W (standard), 0.40 W (power), and 0.50 W (advanced temperature), with a 1000-hour resistance drift (ΔR/R) of 0.10 %, 0.15 %, and 0.25 % respectively. Few flat chips match that stability.
The catch is placement. The round body can roll, so pick-and-place needs a special nozzle and more vacuum, and end-cap solderability varies by finish. Choose MELF when drift, stability, or pulse strength justify the handling cost — precision references, measurement front-ends, and pulse-exposed nodes — and stay with standard chips elsewhere.
Power resistor packages
When dissipation runs past a couple of watts, the package changes job entirely: it exists to move heat into a heatsink or chassis. Formats run from leaded axial parts up through bolt-down aluminum housings.
[IMAGE 3: a TO-220 and a TO-247 resistor bolted to a heatsink beside an aluminum-housed chassis resistor | alt: “power resistor packages: TO-220, TO-247 and aluminum-housed chassis mount”]
| Package | Mounting | Typ. power range | Heatsink for full rating | Example part |
| Axial (through-hole) | PCB leads, self-cooled | 0.25–5 W | No | Metal-oxide / wirewound axial |
| TO-220 | Screw to heatsink | ~20–50 W | Yes | Ohmite TAH20, Arcol AP series |
| TO-247 | Screw to heatsink | ~50–100 W | Yes | Ohmite AP101 (100 W) |
| SOT-227 (ISOTOP) | Bolt to heatsink | 100–300 W | Yes | Ohmite SOT-227 power resistors |
| Aluminum-housed chassis | Bolt to chassis / heatsink | 25–300 W (to 1–2 kW) | Yes | Arcol HS25/HS50/HS100, Ohmite IS (270 W), Riedon UAL (to 300 W) |
Ohmite offers heatsinkable resistors from TO-220 through SOT-227 at 35 W to 200 W, and up to 2 kW with proper heat sinking. The Arcol HS aluminum-housed line rates HS25 = 25 W, HS50 = 50 W, HS100 = 100 W, and the Riedon/Bourns UAL chassis series spans 7.5–50 W with higher-power options to 300 W.
The number that trips people up: that wattage is a heatsinked rating. Ohmite’s HS datasheet specifies the rated power on a standard heatsink at 25 °C, with a hard limit that the resistor’s hot spot must not exceed 200 °C. Bolt the same “50 W” part to a small bracket in a warm box and it may only handle 15–20 W before that hot-spot limit is reached. Always mount to the specified thermal resistance, apply heatsink compound, and read the derating curve — do not trust the label.
How to choose a resistor package
Work the problem in this order, and the package usually picks itself.
- Compute the worst-case dissipation. Use P = I²R or P = V²/R at the highest expected current or voltage, then add 50–100 % margin for peaks and ambient.
- Set the size floor from power and ambient. Match the derated power (not the 70 °C headline) to a chip size; if you need more than ~1 W, look at 2512, a high-power chip variant, or a power package.
- Check the voltage ceiling. For nodes above ~150–200 V, let package length set the choice regardless of power.
- Decide chip vs MELF. If TCR, long-term stability, or pulse strength is critical, step to MELF and accept the placement cost.
- Confirm assembly fit. For hand builds, stay at 0603 or larger. For power parts, verify you have the heatsink area and mounting the rating assumes.
Design mistakes that cause returns
- Sizing to the 70 °C power rating and ignoring enclosure ambient, so the part runs hot and drifts.
- Confusing metric and imperial codes — ordering a metric 0603 (imperial 0201) for an imperial-0603 footprint.
- Trusting a power resistor’s nameplate watts without the heatsink and mounting that rating requires.
- Ignoring the voltage ceiling on high-value dividers, where a small package arcs or drifts under bias.
- Drawing pads from body dimensions instead of a proper land pattern with fillets and tolerance.
- Hand-placing 0402 and smaller on boards that will need manual rework, driving tombstoning and misalignment.
FAQ
What are the standard SMD resistor sizes?
The common chip sizes are 01005, 0201, 0402, 0603, 0805, 1206, 1210, 2010, and 2512. The code is the body’s length and width — imperial in hundredths of an inch, metric in tenths of a millimeter. 0402 through 1206 cover most general-purpose designs, with 0603 the usual default.
Is imperial 0603 the same as metric 0603?
No. Imperial 0603 is 1.6 mm × 0.8 mm. Metric 0603 is 0.6 mm × 0.3 mm, which equals imperial 0201. They are different parts. Always confirm whether a code is imperial or metric before drawing a footprint or ordering, and label your BOM with both.
How much power can an 0805 or 1206 resistor handle?
A standard thick-film 0805 is rated 0.125 W and a 1206 is rated 0.25 W, both at 70 °C ambient, per Vishay CRCW…C e3. Above 70 °C they derate linearly to zero at 155 °C, so real capacity in a hot enclosure is lower. High-power variants raise these figures in the same footprint.
What is a MELF resistor and when should I use it?
MELF is a cylindrical film resistor with metal end caps. Its shape spreads heat and lowers temperature drift — 25–50 ppm/K versus over 200 ppm/K for typical chips — and improves pulse handling. Use it in precision, low-drift, or pulse-exposed circuits, and accept that its round body is harder to place.
Do power resistors really need a heatsink?
For their rated wattage, usually yes. A TO-220, TO-247, or aluminum-housed resistor’s rating assumes heatsink mounting at 25 °C, with a hot spot kept under about 200 °C per Ohmite’s HS data. In free air the same part handles far less, so mount it as the datasheet specifies or derate hard.
Can I replace an 0805 resistor with an 0603 or 1206?
Sometimes. An 0603 can sit on many 0805 pads with careful soldering, but power and voltage headroom drop. Going up to 1206 rarely fits an 0805 land pattern without changes. The resistance value and tolerance must match regardless, and for production, match the footprint rather than force a swap.
The bottom line
Start with the worst-case power and ambient, then let the numbers choose. For general-purpose work, default to a 0603 or 0805 chip and size up only for power or voltage. When temperature drift or pulses matter, step to MELF (0204) and plan for the placement cost. Past a couple of watts, move to a power package — and size it around the heatsink and mounting its rating assumes, not the wattage on the label.
