100 Ohm Resistor Color Code — RC Timing & Power Dissipation

100 Ω in the color code system

Brown · Black · Brown · Gold means digits 1 · 0 with multiplier ×10 → 100 Ω. This page focuses on RC networks and power — not LEDs (see 220 Ω) or pull-ups (10 kΩ).

4-band: Brown · Black · Brown · Gold → 10 × 10 = 100 Ω (±5%) · 5-band (±1%): Brown · Black · Black · Black · Brown → 100 × 1 = 100 Ω (±1%)

Tolerance window (±5%): 95 Ω – 105 Ω · Calculator

RC time constants with 100 Ω (pick a cap, get a time)

Capacitor	$\tau = R × C$	Typical use
100 nF	10 µs	Fast debounce / spike filter
1 µF	100 µs	Soft-start, short delay
10 µF	1 ms	Button debounce (with firmware)
100 µF	10 ms	Power-on reset helper (with MCU)

Example: 100 Ω + 1 µF → $\tau = 100 Ω × 1 µF = 100 µs$. Five time constants ($5\tau$) ≈ 0.5 ms to reach ~99% of final voltage.

Pair identified 100 Ω parts in networks using the parallel/series calculator.

Power dissipation at common rail voltages

100 Ω is low enough that wattage matters on 12 V+ rails:

Voltage across 100 Ω	Current	Power $V^2/R$	Min. rating
3.3 V	33 mA	0.11 W	1/4 W OK
5 V	50 mA	0.25 W	1/4 W marginal — use 1/2 W
12 V	120 mA	1.44 W	Need ≥2 W or different R

Color code tells you value, not wattage — check body size (1/4 W vs 1/2 W) separately.

100 Ω vs 1 kΩ vs 10 Ω (digit/multiplier traps)

You want	Bands	Common error
100 Ω	Brown · Black · Brown	Confused with 1 kΩ (red multiplier)
10 Ω	Brown · Black · Black	Missing one brown band
1 kΩ	Brown · Black · Red	Red adds a zero

5-band precision parts

Metal-film 100 Ω ±1%: Brown · Black · Black · Black · Brown → 100 × 1 = 100 Ω (±1%). Range: 99 Ω – 101 Ω. Use these when matching divider legs — see 1 kΩ divider guide.

FAQ

What colors are on a 100 ohm resistor?

Brown (1), Black (0), Brown (×10), Gold (±5%).

When would I pick 100 Ω over 220 Ω?

When you need lower impedance (RC speed, load) — not for standard 5 V LED indicators.

Related guides (different topics)

• 220 Ω color code — LED brightness vs 330/470 Ω on 5 V

• 1 kΩ color code — divider math & strong pull-ups

• 470 Ω color code — textbook LED history & Y-V family

• Values hub — pick by application

• How to read any resistor (method)

• Decode bands online