Voltage Divider Calculator - Resistor Output Voltage

Agarapu Ramesh — Editor and content reviewer
Editorially reviewed Reviewed by Agarapu Ramesh, science educator (chemistry). LinkedIn
Last reviewed: May 2026 | Ohm's law and standard electrical engineering formulas

A voltage divider splits voltage across two series resistors. The output is taken across the lower resistor. It is a great way to make a reference signal, and a terrible way to power anything that draws real current.

Formula at a glance

  • Vout = Vin x R2 / (R1 + R2)
  • divider current = Vin / (R1 + R2)
  • loaded R2 = R2 in parallel with load resistance

Field note: A divider that measures 5 V with no load may sag badly once a sensor or module is connected. That is not a calculator error. That is loading.

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Voltage Divider Calculator

Calculate output voltage or resistor values

V
Ω
Ω
Result
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Formula

VoutVout = Vin × R2 ÷ (R1+R2)

Circuit Diagram

    Vin ──┬── R1 ──┬── GND
          │        │
          │       Vout
          │        │
          └── R2 ──┘

Related

Ohm's LawVolts to Amps

How to use the Voltage Divider Calculator

Use this as a bench check, then compare it with the part marking, tolerance and a meter reading when the circuit matters. Small components are cheap. Bad assumptions are not.

Worked example

Example: Vin = 12 V, R1 = 14 k ohm and R2 = 10 k ohm gives Vout = 5 V before loading.

Practical checks before you trust the number

  • Keep load resistance much higher than R2, often 10 times or more.
  • Check resistor power if voltage is high.
  • Use a regulator or buffer for loads that draw current.

Common mistake

A divider that measures 5 V with no load may sag badly once a sensor or module is connected. That is not a calculator error. That is loading.

Sources and references

Related calculators

Frequently Asked Questions

V_out = V_in × RI ÷ (RI + RI). Two resistors in series form a divider; the output is taken across RI. Example: 12 V across RI = 8 kΩ and RI = 4 kΩ → V_out = 12 × 4 ÷ 12 = 4 V. Used in sensor scaling, reference voltages, and bias networks.

V_out = V_in × RI ÷ (RI + RI). Memorize this — it's one of the most-used formulas in electronics. The ratio RI ÷ (RI + RI) is the divider ratio. For equal resistors, V_out = V_in ÷ 2.

Pick R values so the bleed current is small enough not to load your supply but large enough to dominate the load you're driving. Typical values: 1 kΩ to 100 kΩ. Higher R wastes less power but is more sensitive to load loading. Always check that the load impedance is at least 10× RI to keep the divider stable.

Because the load draws current from the divider output, which acts in parallel with RI. The effective lower resistance becomes RI I R_load, shifting the divider ratio. If R_load is much smaller than RI, V_out drops significantly. Always design with R_load ≥ 10 × RI, or use a voltage follower op-amp to buffer the output.

Pick RI and RI so V_out = 12 × RI ÷ (RI + RI) = 5. The ratio RI ÷ (RI + RI) = 5/12 = 0.417. So RI ÷ RI = (12 − 5) ÷ 5 = 1.4. Pick RI = 10 kΩ → RI = 14 kΩ (use 15 kΩ standard). Always confirm under load.

Only for very low-current sensors (microamps). For anything drawing real current, the divider voltage will sag because of load loading. Use a voltage regulator (LDO or DC-DC) for any load above a few mA. Voltage dividers are for reference signals, not power.

Yes. Enter desired V_out and V_in, the calculator gives RI/RI ratios. Pick standard E12 or E24 values that come close. Always verify with the loading effect formula: V_out_loaded = V_in × (RI I R_load) ÷ (RI + RI I R_load).