Choose a circuit model, enter values, and calculate Vth. The result appears above this form after submission.
- Select the circuit type that matches your source model.
- Enter component values, including the correct units.
- Choose output unit and decimal precision.
- Press Calculate Vth to display the result above the form.
- Use CSV/PDF export to store the calculation in records.
These sample cases show typical inputs and the expected Thevenin voltage.
| Case | Model | Inputs | Expected Vth |
|---|---|---|---|
| 1 | Divider | Vs=12 V, R1=2 kΩ, R2=4 kΩ | 8.000 V |
| 2 | Divider | Vs=5 V, R1=1 kΩ, R2=1 kΩ | 2.500 V |
| 3 | Current || Rp | Is=20 mA, Rp=150 Ω | 3.000 V |
| 4 | Current || Rp | Is=250 µA, Rp=10 kΩ | 2.500 V |
| 5 | Measured | Voc=3.3 V | 3.300 V |
Values are illustrative. Real networks may require finding Voc at the terminals first.
- Thevenin voltage equals the open-circuit terminal voltage, Voc.
- Divider model is valid when the network reduces to Vs with R1–R2 in series.
- Current source model uses V = I × R for the parallel resistance branch.
- To complete a full Thevenin equivalent, compute Rth separately.
1) What Thevenin Equivalent Voltage Represents
Thevenin equivalent voltage, Vth, is the open-circuit voltage across two terminals of a network. It compresses a complex circuit into a single voltage source used for quick load predictions. In practice, Vth is reported in volts and paired with Rth for complete modeling.
2) Why Open-Circuit Conditions Matter
Open-circuit means no external load current flows at the terminals. That removes voltage drops caused by load current and reveals the network’s driving potential. If a load is connected, the terminal voltage usually falls below Vth depending on Rth and the load resistance.
3) Voltage Divider Networks and Vth
Many sensor and reference circuits reduce to a divider. With a source Vs feeding series resistors R1 and R2, the terminal voltage at the R2 node is Vth = Vs × R2/(R1+R2). For example, Vs=12 V, R1=2 kΩ, R2=4 kΩ gives Vth=8 V.
4) Current Source in Parallel with Resistance
A Norton-like source model often appears in bias networks and small-signal equivalents. When an ideal current source Is is in parallel with Rp, the open-circuit terminal voltage becomes Vth = Is × Rp. If Is=20 mA and Rp=150 Ω, the result is 3 V.
5) Using Measured Voc for Real Circuits
For real prototypes, measuring Voc is sometimes faster than algebra. Disconnect the load, place a voltmeter across the terminals, and record Voc. This calculator lets you enter Voc directly so Vth=Voc. Use a high-impedance meter to reduce measurement error.
6) Units, Scaling, and Precision Controls
Engineering work frequently mixes mV, V, and kV, plus Ω, kΩ, and MΩ. Consistent unit conversion prevents accidental thousandfold mistakes. The output-unit selector converts internally computed volts to your preferred scale, while decimal precision helps match reporting standards or lab sheets.
7) Typical Values and Practical Ranges
In low-power electronics, Vth commonly falls between 0.1 V and 24 V, with resistors from 100 Ω to 1 MΩ. Industrial control signals may use 5–10 V references, while sensor bridges can produce millivolt-level outputs. High-voltage applications should confirm insulation and instrument ratings.
8) Validation, Documentation, and Exports
A quick validation step is to recreate the predicted terminal voltage using the same model and inputs. For divider cases, check that Vth is always less than Vs when R1 is positive. Exporting CSV or PDF captures inputs, units, and results for audits, reports, or troubleshooting logs.
1) Is Vth always the same as Voc?
Yes. By definition, Thevenin equivalent voltage equals the open-circuit terminal voltage measured with no external load connected.
2) How do I find Voc in a complex network?
Remove the load at the terminals, then solve the remaining circuit using node/mesh analysis, superposition, or simulation. The terminal voltage under that condition is Voc.
3) Does the load affect the Thevenin voltage?
The load changes the terminal voltage during operation, but it does not change Vth. Vth is defined only under open-circuit conditions.
4) What if my circuit includes dependent sources?
Vth is still Voc. However, when finding Rth you must keep dependent sources active and use a test source method. This calculator focuses on Vth only.
5) Why can Vth be negative?
A negative value simply indicates polarity opposite to your assumed terminal reference. It can occur with reversed sources, sign conventions, or measured Voc using flipped probe orientation.
6) How is Vth used with Rth?
Together they form the Thevenin model: a source Vth in series with Rth. With a load RL, the load voltage is Vth × RL/(Rth+RL).
7) Are the unit conversions exact?
The scale factors used are standard (mV=10-3 V, kΩ=103 Ω, etc.). Rounding depends on your selected decimal precision and your input measurement uncertainty.