Resistor color bands encode a component’s resistance, tolerance, and sometimes its temperature behavior. With a reliable reading direction and a simple digit-and-multiplier method, you can identify many through-hole resistors used in radio collecting and low-voltage projects.
Start with the resistor and its bands
Color bands are printed around the body of many axial-lead resistors: the leads extend from opposite ends, and the bands run around the cylindrical body. Before decoding, check that the component actually uses a standard resistor color code. Some parts have faded paint, nonstandard markings, or no bands at all; large wirewound resistors, surface-mount parts, and some vintage components may instead use printed numbers or other markings.
A standard code uses these colors for digits:
| Color | Digit | Multiplier |
|---|---|---|
| Black | 0 | ×1 Ω |
| Brown | 1 | ×10 Ω |
| Red | 2 | ×100 Ω |
| Orange | 3 | ×1 kΩ |
| Yellow | 4 | ×10 kΩ |
| Green | 5 | ×100 kΩ |
| Blue | 6 | ×1 MΩ |
| Violet | 7 | ×10 MΩ |
| Gray | 8 | ×100 MΩ |
| White | 9 | ×1 GΩ |
| Gold | — | ×0.1 |
| Silver | — | ×0.01 |
The digit sequence follows the familiar order from black through white. Gold and silver can serve as multipliers, but they are not significant-digit colors in the common band patterns. A tolerance band may also be gold or silver, so identify its role from its position.
Find the reading direction
Most common resistors have four or five bands. The tolerance band is often separated from the others by a noticeably larger gap. Hold the resistor so that this separated band is on the right, then read the other bands from left to right. Do not rely on the direction of the leads or on a band’s apparent darkness alone.
If there is no clear gap, look for other clues:
- Gold or silver is usually the multiplier or tolerance band, not the first significant digit. A gold or silver band at one end often marks the end from which to begin reading.
- The first band is usually closer to one lead than the last band is to the other, though spacing varies.
- Compare the likely decoded value with the circuit diagram, parts list, or a matching component in the same equipment.
- If the direction remains ambiguous, record both possible readings and measure the resistor before deciding.
Aging, heat, dust, and old coatings can make colors difficult to distinguish. Use a bright neutral light and rotate the part to inspect the band all the way around. If the component has been removed from the circuit, clean only as appropriate for its material and condition; avoid scraping or solvents that might damage old coatings or markings.
Decode a four-band resistor
In the four-band code, the first two bands are significant digits, the third is the multiplier, and the fourth gives tolerance. Join the first two digits, then multiply by the third band’s value.
For example, red-violet-orange-gold means:
- Red is 2; violet is 7, giving 27.
- Orange is ×1,000, so 27 × 1,000 = 27,000 ohms, or 27 kΩ.
- Gold indicates ±5% tolerance.
A brown-black-red-gold resistor is 10 × 100 = 1,000 Ω, or 1 kΩ, with ±5% tolerance. A yellow-violet-gold-gold resistor is 47 × 0.1 = 4.7 Ω, with ±5% tolerance. The gold multiplier is useful for low resistance values; it does not mean the resistor has a value of zero.
For very low values, silver can be the multiplier. For instance, brown-black-silver-gold is 10 × 0.01 = 0.1 Ω, with ±5% tolerance. Such values can be hard to measure accurately with an ordinary handheld meter because lead and contact resistance may be comparable to the resistor itself.
Decode five- and six-band resistors
A five-band resistor usually has three significant digits, then a multiplier, then tolerance. Read the first three bands as a three-digit number; multiply by the fourth band and use the fifth as tolerance.
For example, brown-black-black-red-brown is 100 × 100 = 10,000 Ω, or 10 kΩ, with ±1% tolerance. Five bands are common on precision parts, but the band count alone does not prove the component’s function or exact specification.
A six-band resistor adds a temperature-coefficient band after the tolerance band. The first five bands are decoded as above; the sixth specifies how much the resistance changes with temperature, commonly expressed in parts per million per degree Celsius (ppm/°C). Brown is often used for 100 ppm/°C in this code, but confirm the applicable manufacturer or industry marking standard when the exact coefficient matters. A six-band code does not directly state a power rating, maximum voltage, or safety approval.
Tolerance colors commonly encountered include brown for ±1%, red for ±2%, green for ±0.5%, blue for ±0.25%, violet for ±0.1%, gray for ±0.05%, gold for ±5%, and silver for ±10%. No tolerance band commonly indicates ±20% in older or basic coding conventions. Standards and component families can differ, so treat a decoded tolerance as a clue to the marked nominal specification, not proof of the part’s age or provenance.
Check the reading with a multimeter
Color bands give the nominal value, while a meter measures the part’s present resistance. If practical, disconnect at least one lead from the circuit before measuring. Parallel paths through other components can make an in-circuit reading lower or otherwise different from the resistor’s own value.
- Switch the meter to resistance (Ω), choosing a range that can cover the expected value if the meter is not autoranging.
- Touch the probes together briefly to see whether the display responds normally; some meters show a small lead resistance.
- Place one probe on each resistor lead. Keep fingers off the exposed metal during the reading, especially when measuring high resistance.
- Wait for the display to settle and compare the result with the marked value and tolerance.
For a 1 kΩ resistor marked ±5%, an isolated reading from 950 Ω through 1,050 Ω is within that nominal tolerance range, assuming a suitable meter and a stable component. A reading outside the range may mean the resistor has drifted, the contacts are poor, the meter range is wrong, or the resistor is still connected to other circuit paths. For very low ohms, use a meter with an appropriate low-resistance method and account for lead resistance; a basic two-probe meter may not resolve the value well.
A multimeter cannot tell you the resistor’s power rating, voltage rating, pulse capability, or original manufacturer. It also cannot establish that a component is safe to reuse in a high-voltage or mains-connected circuit. Follow the equipment’s service information and use components with suitable electrical and physical ratings.
Apply the code in radio collecting and low-voltage projects
When identifying a resistor in a vintage radio, first determine whether the set is disconnected from power. Some radio circuits contain capacitors that can retain charge after unplugging; use the service manual’s safety procedure and appropriate equipment before working inside. If you are unsure how to make the equipment safe, get help from someone experienced with that type of circuit.
Once safe to inspect, photograph the component and note its location and connections before removing anything. Use the schematic or parts list to cross-check the expected value. Resistors can be original, previously replaced, or altered during earlier repairs, and a color code alone cannot establish which. Record the measured value separately from the color-coded nominal value.
For a low-voltage breadboard or hobby circuit, decode the value before installation and check the circuit’s required resistance and power dissipation. A resistor with the right ohmic value can still be unsuitable if its power rating, voltage rating, tolerance, or temperature behavior does not fit the circuit. When substituting, compare all relevant ratings and the physical spacing or lead arrangement.
Useful workbench aids include:
- A printed color-code reference kept near the meter.
- A magnifier or phone camera for small, closely spaced bands.
- Neutral white lighting to distinguish similar faded colors.
- A notebook or labeled parts tray for recording decoded and measured values.
- The equipment service manual, schematic, and manufacturer data when available.
Troubleshoot ambiguous or unexpected readings
Two colors look alike. Red and brown, or violet and blue, can be difficult to distinguish on dark or aged coatings. Change the lighting angle, use magnification, and compare the result against the circuit’s documented value. Avoid deciding from a phone image alone because automatic white balance can shift colors.
The band pattern reads in two directions. Recheck spacing and look for a gold or silver band that could indicate an end. Then compare each candidate value with the schematic or measure the isolated resistor. Do not force a reading just because one value seems more familiar.
The meter reading is far from the decoded value. Verify the meter is in resistance mode and that its range covers the value. Check probe contact, isolate a lead if safe and practical, and allow the reading to settle. A resistor that has overheated, cracked, become corroded, or drifted with age may no longer measure within tolerance.
The component has markings that do not fit the table. It may use a different code, be a non-resistor, or have markings intended for a specialized part. Check a parts list, datasheet, or service manual rather than applying the standard axial resistor code to every banded component.
The decoded value seems plausible but the replacement still fails. Recheck the circuit function and the required wattage, voltage, tolerance, and temperature characteristics. Also inspect adjacent components and wiring; a resistor can fail because of another fault. Replacing it with the same nominal resistance alone may not address the cause.
Limits of color-code identification
The code gives a nominal resistance and, depending on the band pattern, tolerance and temperature coefficient. It does not encode every property needed to select a replacement. Power rating is often inferred from body size or specified in documentation, but size alone is only a rough guide, particularly when comparing different resistor technologies. For restoration work, identify the circuit position and consult the manufacturer’s service information when available.
Some older parts use faded, unusual, or manufacturer-specific markings. If the bands have deteriorated, the resistor remains connected in circuit, or the equipment’s documentation is missing, the result may stay uncertain. Mark that uncertainty in your repair notes and use circuit analysis or qualified assistance where the consequence of a wrong value could be serious.