Resistor Calculator

Using the calculator is straightforward. Select the color of each band on your resistor from the dropdown menus, working left to right just as they appear on the physical component. The calculator will display the resistance value in ohms, along with the tolerance range.

A few things to keep in mind before you start:

• Identify the number of bands first. Most resistors have 4 bands, but precision resistors use 5 or 6. The calculator supports all three formats.
• Orient the resistor correctly. The first band is typically closest to one end of the resistor body. If there's a gap between the last band and the others, that gap side is the end you read last.
• The last band is always tolerance (and on a 6-band resistor, the band before it is temperature coefficient). Make sure you're assigning colors to the right fields.

Once you've selected all the colors, the result updates automatically. You'll see the nominal resistance value and the plus-or-minus tolerance expressed in ohms and as a percentage.

The color code system for resistors was standardized decades ago and hasn't changed much since. Each color maps to a digit from 0 to 9, and those digits combine to express a resistance value. There's also a multiplier band that scales the value up or down, and a tolerance band that tells you how close the actual component will be to that stated value.

Here's the core digit-to-color mapping:

A popular memory trick is the mnemonic "BB ROY of Great Britain had a Very Good Wife" (Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Gray, White). Corny? Sure. But it works.

The multiplier band uses the same color scale but represents a power of ten. So a red multiplier means multiply by 100 (10²). Gold and silver are also used as multipliers: gold means multiply by 0.1, and silver means multiply by 0.01. Those appear on low-value resistors.

The 4-band resistor is the most common type you'll run into, especially in general-purpose through-hole components. Reading it is simple once you know the structure.

• Band 1: First significant digit
• Band 2: Second significant digit
• Band 3: Multiplier
• Band 4: Tolerance

To calculate the value, take the digits from bands 1 and 2, form a two-digit number, then multiply by the value of band 3. For example, if band 1 is yellow (4), band 2 is violet (7), and band 3 is red (multiply by 100), the resistance is 47 × 100 = 4,700 ohms, or 4.7 kΩ. A gold tolerance band means ±5%.

That's it. Two digits, one multiplier, one tolerance. The math takes about five seconds once the color-to-digit mapping is in your head. The trickier part is often just identifying the colors accurately, especially brown versus red or orange versus yellow under certain lighting conditions.

Precision resistors add more bands to give you a tighter, more specific value. The 5-band resistor is common in applications where ±1% or better accuracy matters.

The structure of a 5-band resistor:

• Band 1: First significant digit
• Band 2: Second significant digit
• Band 3: Third significant digit
• Band 4: Multiplier
• Band 5: Tolerance

So instead of a two-digit base number, you get three digits before the multiplier. A resistor with bands brown (1), black (0), black (0), red (×100), brown (±1%) gives you 100 × 100 = 10,000 ohms, or 10 kΩ at ±1% tolerance.

The 6-band resistor takes this one step further by adding a temperature coefficient band at the end. This band tells you how much the resistance drifts as temperature changes, expressed in parts per million per degree Celsius (ppm/°C). Brown typically represents 100 ppm/°C, red is 50 ppm/°C, and orange is 15 ppm/°C. This matters in precision analog circuits, test equipment, and anything that needs to stay accurate across a range of operating temperatures.

For most hobbyist and general electronics work, you won't encounter 6-band resistors often. But knowing what that extra band means is useful if you ever do.

Here's a complete reference chart covering digits, multipliers, tolerance values, and temperature coefficients for all standard colors.

Keep in mind that not every color appears in every column. Gold and silver, for instance, are only used as multipliers and tolerance indicators, never as digit values. And the temperature coefficient column only applies to 6-band resistors.

Once you know what each band represents, the actual calculation is basic arithmetic.

For a 4-band resistor, the formula looks like this:

Resistance = (Digit1 × 10 + Digit2) × Multiplier

For a 5-band resistor, add one more digit:

Resistance = (Digit1 × 100 + Digit2 × 10 + Digit3) × Multiplier

Let's work through a couple of real examples.

• Example 1 (4-band): Brown, Black, Orange, Gold. That's 1, 0, ×1,000, ±5%. So (10) × 1,000 = 10,000 ohms = 10 kΩ ±5%.
• Example 2 (5-band): Red, Violet, Green, Brown, Brown. That's 2, 7, 5, ×10, ±1%. So (275) × 10 = 2,750 ohms = 2.75 kΩ ±1%.

Resistance values are expressed in ohms (Ω), kilohms (kΩ = 1,000 Ω), or megohms (MΩ = 1,000,000 Ω). When you're working with components in a circuit, it's worth converting to the same unit across the board to avoid off-by-a-thousand mistakes. Those happen more often than you'd think.

Tolerance tells you how far off the actual resistance of a component can be from its labeled value. A resistor marked as 10 kΩ with ±5% tolerance could actually measure anywhere from 9,500 ohms to 10,500 ohms and still be within spec.

Common tolerance values and what they mean in practice:

• ±1% (Brown): Precision resistors. Used in op-amp circuits, measurement equipment, anything where accuracy counts.
• ±5% (Gold): The most common general-purpose tolerance. Fine for LED current limiting, voltage dividers, pull-up resistors, and most basic circuits.
• ±10% (Silver): Older and less common today. Still shows up in vintage gear and low-cost applications.

For most digital circuits, ±5% is completely fine. Microcontrollers don't care if your pull-up resistor is 9.8 kΩ instead of exactly 10 kΩ. But in analog circuits, especially those involving amplifiers or precise voltage references, the tolerance of every resistor in the signal path can genuinely affect the output. In those cases, ±1% components are worth the small extra cost.

One thing to keep in mind: tolerance describes the manufacturing spread, not how the component behaves over time or temperature. A resistor within tolerance today can drift slightly as it ages or heats up. That's where the temperature coefficient (in 6-band resistors) becomes relevant.

Resistors don't come in every possible value. They're manufactured in standardized series, the most common being the E12 and E24 series. E12 gives 12 values per decade (like 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82), and E24 doubles that to 24. Higher-precision series like E96 and E192 exist for tight-tolerance applications.

Here are some of the most frequently used resistor values and where you'll typically see them:

If you're just starting out building circuits, a resistor kit with common values in the E24 series will cover the vast majority of projects you'll encounter. The 10 kΩ resistor alone shows up in nearly every beginner circuit, so it's worth having plenty on hand.

When you're picking a resistor for a specific job, always check both the value and the power rating. The color bands tell you the resistance, but the physical size of the component usually hints at the wattage it can handle. A tiny 1/4W resistor is fine for signal-level work, but drop it into a high-current path and you'll know pretty quickly.