LED resistor for 9 V
Resistor values for LEDs on 9 V PP3 batteries and 9 V wall adapters (guitar pedals, toys, kits). The tables use typical forward voltages and round up to the next standard value, so the LED never gets more current than the target. The calculator is preset to 9 V — change the LED or current to suit your part.
9 V LED resistor table at 20 mA
20 mA is the classic rating for 3 mm and 5 mm indicator LEDs. Formula: R = (9 − Vf) ÷ 0.020.
| LED color | Vf | Exact | E12 (up) | E24 (up) | Actual current | Power → rating |
|---|---|---|---|---|---|---|
| Red / orange | 2 V | 350 Ω | 390 Ω | 360 Ω | 19.4 mA | 140 mW → 1/2 W |
| Yellow | 2.1 V | 345 Ω | 390 Ω | 360 Ω | 19.2 mA | 130 mW → 1/2 W |
| Green (traditional) | 2.2 V | 340 Ω | 390 Ω | 360 Ω | 18.9 mA | 130 mW → 1/2 W |
| True green | 3 V | 300 Ω | 330 Ω | 300 Ω | 20 mA | 120 mW → 1/4 W |
| Blue / white | 3.2 V | 290 Ω | 330 Ω | 300 Ω | 19.3 mA | 110 mW → 1/4 W |
9 V LED resistor table at 10 mA
Modern LEDs are bright at 10 mA or less, and half the current doubles the resistor value and halves its heat.
| LED color | Vf | Exact | E12 (up) | E24 (up) | Actual current | Power → rating |
|---|---|---|---|---|---|---|
| Red / orange | 2 V | 700 Ω | 820 Ω | 750 Ω | 9.33 mA | 65 mW → 1/4 W |
| Yellow | 2.1 V | 690 Ω | 820 Ω | 750 Ω | 9.2 mA | 63 mW → 1/4 W |
| Green (traditional) | 2.2 V | 680 Ω | 680 Ω | 680 Ω | 10 mA | 68 mW → 1/4 W |
| True green | 3 V | 600 Ω | 680 Ω | 620 Ω | 9.68 mA | 58 mW → 1/8 W |
| Blue / white | 3.2 V | 580 Ω | 680 Ω | 620 Ω | 9.35 mA | 54 mW → 1/8 W |
LEDs in series on 9 V
The most LEDs one resistor can serve while still leaving at least 1 V across it (so the current stays predictable), with the resistor for 20 mA. Efficiency is the share of supply power that reaches the LEDs.
| LED color | Max in series | LED voltage | Resistor (power) | Efficiency |
|---|---|---|---|---|
| Red / orange | 4 | 8 V | 51 Ω (20 mW) | 89% |
| Yellow | 3 | 6.3 V | 150 Ω (49 mW) | 70% |
| Green (traditional) | 3 | 6.6 V | 120 Ω (48 mW) | 73% |
| True green | 2 | 6 V | 150 Ω (60 mW) | 67% |
| Blue / white | 2 | 6.4 V | 130 Ω (52 mW) | 71% |
When the supply is not exactly 9 V
Current with the 20 mA resistor from the table above (360 Ω for red, 300 Ω for white) at the voltages this supply really sees:
| Condition | Supply | Red LED | White LED |
|---|---|---|---|
| Fresh alkaline battery | 9.6 V | 21.1 mA | 21.3 mA |
| Nominal | 9 V | 19.4 mA | 19.3 mA |
| Half-used battery | 7.8 V | 16.1 mA | 15.3 mA |
| Nearly flat (6 × 0.9 V cells) | 5.4 V | 9.44 mA | 7.33 mA |
Notes for 9 V circuits
A 9 V battery is six 1.5 V cells in series, so its voltage falls steadily from about 9.6 V when new to about 5.4 V when it is considered flat. The supply-variation table shows what that does to the current: with a resistor sized at 9 V, a single red LED drops to well under half its current as the battery empties. That is normal and harmless — the LED simply gets dimmer.
A 9 V battery holds only a few hundred milliamp-hours, so every milliamp counts. At 10 mA a single LED drains it in roughly two days of continuous use; at 2–3 mA it lasts over a week. Putting LEDs in series is the efficient choice here: three red LEDs share the same current that one would use, and the resistor wastes less voltage.
Other supplies: 3.3 V · 5 V · 12 V · 24 V. The method and edge cases are explained in the LED resistor guide, and wattage in resistor power ratings.
FAQ
What resistor do I need for an LED on 9 V?
For a red LED (≈2 V) at 20 mA: (9 − 2) ÷ 0.02 = 350 Ω, so use 360 Ω. For a blue or white LED (≈3.2 V) at 20 mA: 290 Ω, so 300 Ω. At 10 mA a red LED needs 750 Ω.
What wattage resistor for an LED on 9 V?
A red LED at 20 mA puts 140 mW into a 360 Ω resistor, so use 1/2 W or larger (twice the dissipated power).
How many LEDs can I run in series on 9 V?
Leaving at least 1 V for the resistor: 4 × red / orange, 3 × yellow, 3 × green (traditional), 2 × true green, 2 × blue / white.
How long will a 9 V battery run an LED?
A typical alkaline 9 V battery holds around 400–600 mAh at low current. At 20 mA that is roughly 20–30 hours; at 5 mA several days. Put LEDs in series to light more of them from the same current.