LED Series Resistor and Current Bounds Calculator
Calculate an ideal one-string resistor or current and compare entered supply, forward-drop and resistor-tolerance corners.
YOUR CALCULATION
Result
—
Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Subtract the string forward drops from supply. Divide headroom by target current for an ideal resistor, or by entered resistor for current. Evaluate extreme headroom and resistance corners.
R=(Vs−nVf)/I; Imax=max(0,Vs,max−nVf,min)/(R(1−tolerance))
Worked example
One LED at entered 2 V forward drop, 5 V supply and 10 mA target gives an ideal 300 Ω resistor and nominal resistor dissipation 0.03 W.
Assumptions and input details
One series string only. Forward drops, supply range, target and tolerance are user-entered assumptions, not part recommendations. Constant forward-drop approximation ignores the current/temperature-dependent diode curve. Zero headroom gives zero modeled current, without modeling reverse behavior. No selected standard resistor series, component ratings, thermal derating or brightness prediction.
References: ROHM: forward voltage and series LED resistor circuit
Unit definitions
Unit selection is independent of language. Each selector contains only units for its physical quantity. Calculations use defined base units internally.
SI prefixes are explicit: for example, milli means one thousandth, micro one millionth and kilo one thousand. Changing a unit changes the interpretation of the entered number.
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
Enter two electrical quantities to find voltage, current, resistance and power for an ideal DC resistor. Follow the equations and current–voltage graph.
Compare unloaded and resistively loaded divider voltage, branch currents and dissipation.
Compare inverting/non-inverting resistor gain around a reference and apply your entered output-voltage bounds.
Reserved advertising space.