Buck Converter Calculator — Duty Cycle & Inductor Sizing
Find the output voltage, power budget, and minimum CCM inductance for a step-down switching regulator. Enter input voltage, duty cycle, load current, switching frequency, and estimated efficiency.
V
%
A
kHz
%
Vout = Vin × D (ideal steady-state output)
- 1
Duty cycle (fraction)
50 % ÷ 100 = 0.5 - 2
Output voltage
12 × 0.5 = 6
How does this calculator work?
A step-down (buck) converter produces Vout = Vin × D, where D is duty cycle (0–1). Minimum CCM inductance is Lmin = (Vin − Vout) × D / (2 × f × Iout). Power loss = Pin − Pout = Vout × Iout × (1/η − 1). Enter duty cycle, load, and frequency to size the inductor and check the power budget.
Formula
How this is calculated
A buck converter switches an input supply through an inductor and diode at high frequency. The duty cycle D — the fraction of each period the high-side switch is on — sets the average output voltage: Vout = Vin × D. With an efficiency factor η (accounting for FET, diode, and winding losses), the average input current is Iin = (Vout × Iout) / (Vin × η) and the power lost is Pin − Pout.
For continuous conduction mode (CCM) — where the inductor current never reaches zero — the inductance must meet Lmin = (Vin − Vout) × D / (2 × f × Iout). A larger inductor reduces peak-to-peak ripple current; operating below Lmin pushes the converter into discontinuous conduction mode (DCM), where the output voltage becomes load-dependent and the control loop more complex.
This calculator uses ideal steady-state equations. Practical designs must also account for output-capacitor ripple voltage (ΔVout ≈ ΔiL / (8 × f × C)), gate-drive and deadtime losses, and parasitic resistances. The Vout–duty-cycle plot shows the linear relationship for your input voltage, useful when tuning the feedback resistors.
Frequently asked questions
Duty cycle D is the fraction of the switching period that the high-side switch is closed, expressed as a percentage. In the ideal buck converter Vout = Vin × D, so 50 % duty cycle on a 12 V input produces 6 V output.
In CCM the inductor current never drops to zero between switching cycles. CCM gives lower peak current, less EMI, and simpler control-loop design. If inductance falls below Lmin the converter enters DCM, where output voltage becomes load-dependent.
Higher frequency reduces Lmin proportionally — doubling f halves the required inductance, enabling much smaller magnetics. The trade-off is that switching losses in the FET and diode increase with frequency, reducing overall efficiency.
Also known as
TG we-Calculate Editorial Team. (2026). Buck Converter Calculator — Duty Cycle & Inductor Sizing [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/buck-converter
TG we-Calculate Editorial Team. "Buck Converter Calculator — Duty Cycle & Inductor Sizing." TG we-Calculate. 2026. https://we-calculate.com/calculator/buck-converter.
TG we-Calculate Editorial Team, "Buck Converter Calculator — Duty Cycle & Inductor Sizing," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/buck-converter
@misc{wecalculate_buck_converter, title = {Buck Converter Calculator — Duty Cycle & Inductor Sizing}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/buck-converter}}, year = {2026}, note = {TG we-Calculate} }
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