Resistor Calculator

Number of Bands

Band 1 — 1st Digit

Band 2 — 2nd Digit

Multiplier Band

Tolerance Band

Select Color Bands to Decode

Use the Color Code tab to select resistor band colors and instantly see the resistance value, tolerance range, and a visual resistor diagram. Switch tabs for series/parallel, voltage divider, or SMD calculations.

Color Band Reference Chart (IEC 60062:2016)

Color	Digit	Multiplier	Tolerance	TCR (ppm/K)
Black	0	×1	—	—
Brown	1	×10	±1%	100
Red	2	×100	±2%	50
Orange	3	×1k	—	15
Yellow	4	×10k	—	25
Green	5	×100k	±0.5%	20
Blue	6	×1M	±0.25%	10
Violet	7	×10M	±0.1%	5
Grey	8	×100M	±0.05%	1
White	9	×1000M	—	—
Gold	—	×0.1	±5%	—
Silver	—	×0.01	±10%	—

Source: IEC 60062:2016 — Marking codes for resistors and capacitors.

Last updated October 20, 2018

Decode resistor color codes, calculate series and parallel combinations, solve voltage dividers, and decode SMD resistor markings

Resistors are among the most fundamental components in electronics, used in virtually every circuit to control current flow, divide voltages, set gain, limit LED current, and form filters. Understanding how to read resistor color codes and calculate resistor combinations is a core skill for electronics hobbyists, students, engineers, and technicians alike. This free Resistor Calculator combines four essential tools in one: a color code decoder for through-hole resistors, a series and parallel resistance calculator, a voltage divider solver, and an SMD (surface mount device) resistor code decoder. The most common task when working with through-hole resistors is reading the color-coded bands printed on the component body. The color code system, standardized by IEC 60062:2016, assigns each color a digit value from 0 (black) to 9 (white), a multiplier value, a tolerance percentage, and for 6-band precision resistors, a temperature coefficient rating in ppm per Kelvin. A standard 4-band resistor has two significant digit bands, one multiplier band, and one tolerance band. For example, Brown-Black-Red-Gold means 1-0 × 100 = 1,000 Ω (1 kΩ) with ±5% tolerance. A 5-band resistor adds a third significant digit for higher precision: Brown-Black-Black-Red-Brown decodes as 1-0-0 × 100 = 10,000 Ω (10 kΩ) at ±1%. The 6-band variant includes a temperature coefficient band that tells you how much the resistance changes with temperature — critical for precision circuits operating across wide temperature ranges. The tolerance band is often misunderstood but extremely important for circuit design. A 1 kΩ resistor with ±5% tolerance could measure anywhere from 950 Ω to 1,050 Ω and still be within specification. For most general-purpose applications this variation is acceptable, but precision circuits — voltage references, instrumentation amplifiers, precision dividers — require tighter tolerances: ±1% (brown) or ±0.5% (green). The calculator shows you the full acceptable range for any resistor, helping you verify that a circuit will function correctly across the entire tolerance range of every component. Series and parallel resistance combinations are fundamental concepts in circuit analysis. When resistors are connected in series — end to end in a chain — the total resistance is simply the sum of all individual values. This is used to achieve resistance values not available in standard series, to distribute voltage drops, or to increase power dissipation capacity. When resistors are connected in parallel — both leads of each resistor connected to the same two nodes — the total resistance is always less than the smallest individual resistor, calculated using the reciprocal sum formula. Parallel combinations are used to achieve low resistance values, increase current-handling capacity, or decrease resistance in steps. This calculator handles up to 8 resistors in either configuration and shows each resistor's proportional contribution as a visual bar chart. The voltage divider is one of the most widely used circuits in electronics. Two resistors connected in series between a supply voltage and ground, with the output taken from the junction between them, produce an output voltage that is a precise fraction of the input. The formula is elegantly simple: Vout = Vin × R2 / (R1 + R2). Voltage dividers appear in sensor interfaces, microcontroller input conditioning, bias networks, level shifting circuits, battery monitoring, and analog reference generation. The calculator shows not just Vout but also the divider current, voltage across each resistor, and power dissipated in each resistor — the last two being critical for checking that resistors are within their power ratings. SMD (surface-mount) resistors are too small to print color bands, so they use a numeric or alphanumeric code stamped on the component body. In the 3-digit system, the first two digits are significant figures and the third digit is the number of zeros to append. For example, '472' means 47 followed by two zeros = 4,700 Ω = 4.7 kΩ. The 4-digit system works the same way with three significant digits: '1002' means 100 followed by two zeros = 10,000 Ω = 10 kΩ. Values below 10 Ω are indicated using 'R' as the decimal point: '4R7' means 4.7 Ω. The SMD decoder in this tool handles all these formats automatically. The visual resistor diagram updates in real time as you select color bands, making it easy to verify your band reading before committing to a component selection. The color band reference table at the bottom of the calculator provides the complete IEC 60062 color-to-value mapping in a single glance — digit values, multipliers, tolerances, and temperature coefficients — so you can cross-check any band combination quickly. All calculations run entirely in your browser; no data is ever sent to a server.

Understanding Resistors and Color Codes

What Are Resistor Color Codes?

Resistor color codes are a standardized system (IEC 60062:2016) for marking the resistance value and tolerance of through-hole resistors using colored bands printed on the component body. The system was developed because resistors are too small to print numbers on legibly, and color bands remain readable from any orientation. Each color represents a digit (0–9), a multiplier power of ten, a tolerance percentage, or a temperature coefficient. Three-band resistors have two digit bands and a multiplier, implying ±20% tolerance. Four-band is the most common, adding an explicit tolerance band. Five-band precision resistors add a third digit for values like 10.0 kΩ. Six-band resistors add a temperature coefficient band showing how much the resistance drifts with temperature, measured in parts-per-million per Kelvin (ppm/K). Gold and silver are used for multipliers (×0.1 and ×0.01) and for tolerance bands (±5% and ±10%) but never as digit bands.

How Are Resistance Values Calculated?

For 3-band and 4-band resistors, the formula is: R = (D1 × 10 + D2) × Multiplier. The first two color bands give the two significant digits and the multiplier band scales the value. For example, Red(2)-Violet(7)-Orange(×1000) = 27 × 1000 = 27,000 Ω = 27 kΩ. For 5-band and 6-band resistors: R = (D1 × 100 + D2 × 10 + D3) × Multiplier, adding a third significant digit. Tolerance gives the acceptable range: Minimum = R × (1 − T/100), Maximum = R × (1 + T/100). Series combinations: R_total = R1 + R2 + … + Rn. Parallel combinations: R_total = 1 / (1/R1 + 1/R2 + … + 1/Rn). Voltage divider: Vout = Vin × R2 / (R1 + R2). SMD codes: 3-digit 'XYZ' = XY × 10^Z; 4-digit 'XYZW' = XYZ × 10^W.

Why Do Resistor Tolerances and Values Matter?

Resistor tolerance directly affects circuit performance and reliability. In a simple LED current-limiting resistor, a ±5% tolerance on a 470 Ω resistor means the LED current could vary by ±5%, which is usually acceptable. But in a voltage reference divider for an analog-to-digital converter, a ±5% tolerance on each resistor could combine to produce a reference error of up to 10%, making measurements unreliable. Precision circuits require ±1% or tighter resistors. Temperature coefficient matters in environments with wide temperature swings: a 100 ppm/K resistor changes by 0.01% per degree Celsius. Over a 50°C temperature range, this is 0.5% — small but significant for precision work. For voltage dividers, the absolute values matter less than the ratio between R1 and R2, which is why matched resistors from the same tape reel (with correlated tolerances) often perform better than individually selected high-precision parts.

Limitations and Practical Considerations

This calculator uses the nominal resistor value for all calculations. Real resistors are subject to tolerance (variation from nominal), temperature coefficient (drift with temperature), aging (long-term drift), voltage coefficient (resistance changing with applied voltage, significant in metal oxide resistors at high voltages), and self-heating (power dissipation changes resistance). The voltage divider calculator assumes an ideal unloaded divider — in practice, any load connected to Vout will pull current through R2 and reduce Vout below the calculated value. This is the loaded voltage divider effect: the effective R2 becomes R2 in parallel with the load resistance. For accurate results in loaded divider applications, use resistor values much smaller than the load resistance (typically R1 + R2 less than one-tenth the load resistance). Power dissipation values shown are continuous DC dissipation; derate by 50% for reliable long-term operation and follow the resistor's maximum power rating.

Key Formulas

Ohm's Law

V = I × R

Voltage (V) equals current (I) multiplied by resistance (R). Rearranges to I = V/R and R = V/I.

Series Resistance

R_total = R₁ + R₂ + R₃ + … + Rₙ

Total resistance of resistors connected end-to-end is the simple sum of all individual resistance values.

Parallel Resistance

1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + … + 1/Rₙ

For resistors sharing the same two nodes, the reciprocal of total resistance equals the sum of the reciprocals of each resistance.

Power Dissipation

P = I² × R = V² / R = V × I

Electrical power dissipated as heat in a resistor. Critical for selecting the correct power rating (¼W, ½W, 1W, etc.).

Reference Tables

E12 Standard Resistor Values (per decade)

The E12 series contains 12 preferred values per decade, covering ±10% tolerance resistors. Multiply by any power of 10 (×1, ×10, ×100, ×1k, ×10k, ×100k, ×1M).

E12 Value	Multiplied Examples
1.0	1.0 Ω, 10 Ω, 100 Ω, 1 kΩ, 10 kΩ, 100 kΩ, 1 MΩ
1.2	1.2 Ω, 12 Ω, 120 Ω, 1.2 kΩ, 12 kΩ, 120 kΩ, 1.2 MΩ
1.5	1.5 Ω, 15 Ω, 150 Ω, 1.5 kΩ, 15 kΩ, 150 kΩ, 1.5 MΩ
1.8	1.8 Ω, 18 Ω, 180 Ω, 1.8 kΩ, 18 kΩ, 180 kΩ, 1.8 MΩ
2.2	2.2 Ω, 22 Ω, 220 Ω, 2.2 kΩ, 22 kΩ, 220 kΩ, 2.2 MΩ
2.7	2.7 Ω, 27 Ω, 270 Ω, 2.7 kΩ, 27 kΩ, 270 kΩ, 2.7 MΩ
3.3	3.3 Ω, 33 Ω, 330 Ω, 3.3 kΩ, 33 kΩ, 330 kΩ, 3.3 MΩ
3.9	3.9 Ω, 39 Ω, 390 Ω, 3.9 kΩ, 39 kΩ, 390 kΩ, 3.9 MΩ
4.7	4.7 Ω, 47 Ω, 470 Ω, 4.7 kΩ, 47 kΩ, 470 kΩ, 4.7 MΩ
5.6	5.6 Ω, 56 Ω, 560 Ω, 5.6 kΩ, 56 kΩ, 560 kΩ, 5.6 MΩ
6.8	6.8 Ω, 68 Ω, 680 Ω, 6.8 kΩ, 68 kΩ, 680 kΩ, 6.8 MΩ
8.2	8.2 Ω, 82 Ω, 820 Ω, 8.2 kΩ, 82 kΩ, 820 kΩ, 8.2 MΩ

Resistor Power Ratings by Package Size

Maximum continuous power dissipation for common through-hole and SMD resistor packages at 25°C ambient.

Package	Type	Power Rating	Typical Use
0201	SMD	1/20 W (50 mW)	Ultra-compact mobile devices
0402	SMD	1/16 W (62.5 mW)	High-density PCBs, smartphones
0603	SMD	1/10 W (100 mW)	General-purpose SMD circuits
0805	SMD	1/8 W (125 mW)	Standard SMD, most common size
1206	SMD	1/4 W (250 mW)	Higher power SMD applications
2512	SMD	1 W	Power sensing and current limiting
1/4 W axial	Through-hole	1/4 W (250 mW)	Most common hobby/prototyping resistor
1/2 W axial	Through-hole	1/2 W (500 mW)	Moderate power circuits
1 W axial	Through-hole	1 W	Power supply and load resistors
2 W axial	Through-hole	2 W	High-current LED drivers, power amps

Worked Examples

Current Through a 470 Ω Resistor at 5V

A 470 Ω resistor is connected across a 5V DC supply. Find the current flowing through it and the power dissipated.

Apply Ohm's Law: I = V / R = 5 / 470 = 0.01064 A ≈ 10.64 mA

Calculate power: P = V × I = 5 × 0.01064 = 0.05319 W ≈ 53.2 mW

Alternatively: P = V² / R = 25 / 470 = 0.05319 W ≈ 53.2 mW

A standard 1/4 W (250 mW) resistor is more than adequate for this 53.2 mW dissipation.

The current is 10.64 mA and the power dissipated is 53.2 mW. A standard 1/4 W through-hole resistor or 0805 SMD package handles this comfortably.

Parallel Combination of 100 Ω and 220 Ω

Two resistors — 100 Ω and 220 Ω — are connected in parallel. Find the total resistance.

Apply the parallel formula: 1/R_total = 1/R₁ + 1/R₂ = 1/100 + 1/220

Calculate each reciprocal: 1/100 = 0.01, 1/220 = 0.004545

Sum the reciprocals: 0.01 + 0.004545 = 0.014545

Take the reciprocal of the sum: R_total = 1 / 0.014545 = 68.75 Ω

The parallel combination is 68.75 Ω — always less than the smallest individual resistor (100 Ω). This is close to the standard E12 value of 68 Ω.

Voltage Divider for 3.3V from 5V Supply

Design a voltage divider to produce 3.3V from a 5V supply using standard resistor values.

Use the voltage divider formula: Vout = Vin × R₂ / (R₁ + R₂), rearranged to R₁/R₂ = (Vin/Vout) − 1 = (5/3.3) − 1 = 0.515

Choose R₂ = 10 kΩ (standard value), then R₁ = 0.515 × 10,000 = 5,150 Ω

Nearest standard E12 value for R₁ is 5.1 kΩ (available in E24 series) or 4.7 kΩ

With R₁ = 4.7 kΩ and R₂ = 10 kΩ: Vout = 5 × 10,000 / (4,700 + 10,000) = 3.40 V

Divider current: I = 5 / (4,700 + 10,000) = 0.34 mA — very low power consumption

Using R₁ = 4.7 kΩ and R₂ = 10 kΩ produces 3.40V (close to 3.3V target) with only 0.34 mA of quiescent current. For a more precise 3.3V, use R₁ = 5.1 kΩ.

How to Use the Resistor Calculator

Choose Your Calculation Mode

Select the tab matching your task. Use 'Color Code' to decode the colored bands on a through-hole resistor and find its value, tolerance range, and temperature coefficient. Use 'Series / Parallel' to calculate the combined resistance of multiple resistors wired together. Use 'Voltage Divider' to find Vout for a two-resistor voltage divider circuit. Use 'SMD Code' to decode the numeric markings on a surface-mount resistor.

Enter the Resistor Details

In Color Code mode, first select the number of bands (3, 4, 5, or 6) then pick each band color from the dropdowns. A color swatch previews your selection and the visual resistor diagram updates in real time. In Series/Parallel mode, type each resistor value and select its unit (Ω, kΩ, or MΩ) — add up to 8 resistors using the 'Add Resistor' button. In Voltage Divider mode, enter Vin, R1, and R2 with their units. In SMD mode, type the code printed on the component.

Review the Results

Results appear instantly as you make selections. The Color Code result shows the decoded resistance, tolerance percentage, and the full acceptable range from minimum to maximum resistance — useful for verifying that your circuit will work across all component variations. The tolerance visualization bar shows the spread graphically. Series/Parallel results include a bar chart showing each resistor's proportional contribution to the total. Voltage Divider results include a donut chart showing the voltage split and power dissipation in each resistor.

Export or Copy Your Results

Use the 'Copy Value' button to copy the resistance value to your clipboard for use in datasheets or calculation notes. Use 'Export CSV' to download all result details as a spreadsheet-compatible file. Use 'Print' to generate a clean printout of the results. The IEC 60062 Color Band Reference Chart at the bottom of the page is always visible and provides a quick lookup for all colors, digits, multipliers, tolerances, and TCR values.

Frequently Asked Questions

How do I read a 4-band resistor color code?

Hold the resistor with the tolerance band (gold or silver) on the right. Read the bands from left to right. The first band gives the first digit (0–9), the second band gives the second digit, the third band is the multiplier (the power of ten to multiply by), and the fourth band (gold or silver) is the tolerance. Multiply the two-digit number formed by bands 1 and 2 by the multiplier. For example: Brown(1)-Black(0)-Orange(×1000)-Gold(±5%) = 10 × 1,000 = 10,000 Ω = 10 kΩ at ±5%. If you cannot determine which end the tolerance band is on, the gap between the last two bands is usually slightly wider than the gaps between the first three bands. This calculator decodes any combination instantly — just select the colors.

What is the difference between 4-band and 5-band resistors?

Both 4-band and 5-band resistors use the same color code system, but 5-band resistors have three significant digit bands instead of two, allowing them to express resistance values with greater precision. A 4-band resistor can express values like 10 kΩ, 12 kΩ, 15 kΩ — typical E12 or E24 series values. A 5-band resistor can express 10.0 kΩ, 10.2 kΩ, 10.5 kΩ — E96 or E192 series values. Five-band resistors are typically precision types with ±1% or tighter tolerance (the tolerance band is brown for ±1%, red for ±2%, green for ±0.5%). The multiplier and tolerance bands are positions 4 and 5 respectively. Six-band resistors add a sixth band for the temperature coefficient, indicating how stable the resistance is across temperature.

Why does parallel resistance always come out lower than the smallest resistor?

When resistors are in parallel, they provide additional paths for current to flow between the two nodes. More current paths means lower total resistance — the circuit appears easier for current to pass through. Mathematically, parallel resistance is calculated as the reciprocal of the sum of reciprocals: 1/R_total = 1/R1 + 1/R2 + ... Each term 1/Rn is the conductance (ease of current flow) through that resistor. Adding more conductances always increases total conductance, which means decreasing total resistance. Even connecting a very large resistor (say, 1 MΩ) in parallel with a small one (100 Ω) reduces the total — the 1 MΩ carries only a tiny amount of extra current but that still means resistance must decrease. This is why short circuits (zero resistance paths) reduce total resistance to nearly zero regardless of other resistors connected in parallel.

How does a voltage divider work and when should I use one?

A voltage divider consists of two resistors in series between a supply voltage (Vin) and ground. The output voltage (Vout) is taken from the junction between the two resistors. Because the current through both resistors is the same (series circuit), and voltage drop is proportional to resistance, the output voltage is a fraction of the input: Vout = Vin × R2/(R1+R2). Voltage dividers are used to level-shift signals (e.g., convert a 5V output to 3.3V for a microcontroller), create bias voltages, measure battery voltage with a microcontroller ADC, set reference levels, and condition sensor outputs. The key limitation is that voltage dividers are unregulated — connecting a load to Vout draws additional current through R2, reducing Vout. For power-supplying applications, use a voltage regulator instead. For signal-level applications where load impedance is much higher than R2, voltage dividers work very well.

How do I decode an SMD resistor code?

Surface-mount resistors (SMD) use printed numeric codes instead of color bands. In the 3-digit system, the first two digits are significant figures and the third digit is the exponent (number of zeros to add). '472' = 47 × 10² = 4,700 Ω = 4.7 kΩ. '100' = 10 × 10⁰ = 10 Ω. '000' and '0000' both mean 0 Ω (jumper). In the 4-digit system, the first three digits are significant figures and the fourth is the exponent. '1002' = 100 × 10² = 10,000 Ω = 10 kΩ. '4703' = 470 × 10³ = 470,000 Ω = 470 kΩ. For values below 10 Ω, 'R' is used as a decimal point: '4R7' = 4.7 Ω, 'R47' = 0.47 Ω. Simply enter any of these formats into the SMD decoder tab and the resistance is decoded instantly.

What does the temperature coefficient (TCR) on a 6-band resistor mean?

The temperature coefficient of resistance (TCR) tells you how much the resistance changes with temperature, expressed in parts per million per Kelvin (ppm/K). A TCR of 100 ppm/K means the resistance changes by 100 parts per million for every 1°C change in temperature — equivalent to 0.01% per degree Celsius. Over a 50°C range, a 100 ppm/K resistor drifts 0.5% from its nominal value. Typical TCR values from the IEC color code: Brown = 100 ppm/K, Red = 50 ppm/K, Orange = 15 ppm/K, Yellow = 25 ppm/K, Green = 20 ppm/K, Blue = 10 ppm/K, Violet = 5 ppm/K, Grey = 1 ppm/K. Low TCR is critical for precision voltage references, instrumentation, and sensors. For general-purpose applications, TCR is rarely critical, but for circuits operating across automotive temperature ranges (−40°C to +125°C) even a modest 100 ppm/K can cause measurable drift that must be accounted for in the design margin.