LED Resistor Calculator
Series resistor ohms and watts for an LED from supply, Vf, and current.
Results
Resistor (exact)
Suggested (round up ~10Ω)
- Power in resistor
- 0.06 W
You might also need
Educational estimates · not financial advice · free, no signup
Formula / how it works
R = (Vsupply − Vf) / I; P = (Vsupply − Vf) × I.
Detailed guide
What it is, how to use it, how to read the numbers, common mistakes, a worked example, formulas, and FAQs.
What this calculator is
Textbook physics/chemistry, SI-friendly. The LED Resistor Calculator on MyCalcsWorld is for homework checks and first-cut estimates under idealized assumptions unless noted. What it does: Find series resistor ohms and power for an LED given supply, Vf, and current. Typical inputs: Supply voltage (V), LED forward voltage Vf (V), LED current (mA). Demo defaults (supply voltage 5 V, led forward voltage vf 2 V, led current 20 mA) currently resolve to Resistor (exact) 150 Ω; Suggested (round up ~10Ω) 150 Ω in the live panel — change any field to explore sensitivity. Who it helps: lab students, makers, and engineers doing first-cut checks with textbook identities before applying real tolerances.
When to use / who it helps
- Quickly checking led resistor numbers without a spreadsheet.
- Comparing scenarios by changing one input at a time.
- Learning the underlying formula with a worked example.
- Sharing a transparent estimate with a teammate or client.
- Use the LED Resistor Calculator for homework checks and first-cut design estimates under textbook assumptions.
How to use
Steps
- Open the calculator and review the default demo values.
- Replace defaults with your own figures in the labeled fields.
- Read the primary emphasized results and any disclaimer notes.
- Optional: tweak one input to see sensitivity.
- Follow related links if you need a companion calculation.
- Open the LED Resistor Calculator on MyCalcsWorld and skim the labeled fields before you type.
How to interpret results
- Emphasized rows are the headline outputs for most users.
- Secondary rows provide cost, unit, or context checks.
- Disclaimers flag educational or illustrative limits — take them seriously.
- Each result is driven only by the labeled inputs (Supply voltage (V), LED forward voltage Vf (V), LED current (mA)); anything not on the form (fees, holidays, clinical adjustments) is outside this estimate.
- Results assume the idealized model stated in the formula notes (constant parameters, ohmic behavior, etc.).
Common mistakes & gotchas
- Mixing units (inches vs feet, percent vs decimal, kg vs lb).
- Treating illustrative defaults as official limits or diagnoses.
- Ignoring fees, waste factors, or holidays that change the real answer.
- Using the output as a substitute for professional advice on regulated topics.
- Mixing SI and customary units across: Supply voltage (V), LED forward voltage Vf (V), LED current (mA).
Worked example
Worked example — 5 V supply, 2 V Vf, 20 mA
- R = 3/0.02 = 150 Ω; power = 0.06 W.
- Open the LED Resistor Calculator (led resistor) and note the starting defaults (supply voltage 5 V, led forward voltage vf 2 V, led current 20 mA).
- Use these labeled inputs (the form defaults): Supply voltage = 5 V; LED forward voltage Vf = 2 V; LED current = 20 mA.
- Read the live result panel. With those defaults, MyCalcsWorld currently reports: Resistor (exact): 150 Ω · Suggested (round up ~10Ω): 150 Ω.
Result: With defaults (supply voltage 5 V, led forward voltage vf 2 V, led current 20 mA), the LED Resistor Calculator shows: Resistor (exact) 150 Ω; Suggested (round up ~10Ω) 150 Ω.
To load the form's own demo values, tap Try example above the Calculate button.
How to calculate / formula
R = (Vsupply − Vf) / I; P = (Vsupply − Vf) × I.
Frequently asked questions
What does the led resistor calculator do?
It computes the labeled outputs from your inputs using the formula note on the page — instantly in the browser.
Are results a professional opinion?
No. MyCalcsWorld provides educational estimates. Confirm regulated or medical decisions with qualified professionals.
Can I change units or defaults?
Yes — edit every field. Advanced or mode selectors appear when a tool supports alternate inputs.
Does this work worldwide?
Math is unit-labeled and currency-aware where marked. Always match local rates, limits, and conventions.
What does the LED Resistor Calculator on MyCalcsWorld actually compute?
Find series resistor ohms and power for an LED given supply, Vf, and current. You enter Supply voltage (V), LED forward voltage Vf (V), LED current (mA), and the result panel updates in your browser.
What inputs does the LED Resistor Calculator need?
The LED Resistor Calculator asks for: Supply voltage (V); LED forward voltage Vf (V); LED current (mA).
What results does the LED Resistor Calculator show?
The panel reports Resistor (exact), Suggested (round up ~10Ω). Each figure is recalculated whenever you change an input, so you can compare scenarios side by side.
Does this include real-world losses and tolerances?
Usually not. Textbook identities assume ideal conditions unless a field asks for efficiency, friction, or tolerance. Apply your own safety factors for designs that affect safety or compliance.
Textbook formulas under ideal assumptions. For safety-critical, structural, or regulated work, verify with a qualified engineer and the governing standards. Full disclaimer