Voltage divider current draw and resistor power
A voltage divider is a continuous load. The resistor pair sets the output ratio, but the absolute values set current draw, source loading, thermal stress, noise sensitivity, and how easily the next circuit can disturb the node.
Reviewed 29 June 2026
How do resistor values affect voltage-divider current and power?
For a fixed divider ratio, lower resistor values draw more current, waste more power, and improve stiffness against leakage or input bias. Higher resistor values save current and dissipate less power, but they are more sensitive to loading, contamination, ADC sampling, and noise pickup.
Model summary
- Ideal output: Vout = Vin * Rbottom / (Rtop + Rbottom).
- Divider current: Idivider = Vin / (Rtop + Rbottom).
- Top resistor power: Ptop = Idivider^2 * Rtop.
- Bottom resistor power: Pbottom = Idivider^2 * Rbottom.
- Equivalent output resistance: Rout = Rtop parallel Rbottom, before the receiving circuit is connected.
Worked example
For Vin = 12 V, Rtop = 10 kOhm, and Rbottom = 10 kOhm, the output is 6 V and the divider current is 12 V / 20 kOhm = 0.6 mA.
Each resistor dissipates I^2 * R = 0.6 mA squared times 10 kOhm = 3.6 mW.
Changing both resistors to 100 kOhm keeps the 6 V ratio but reduces current to 60 microamps and power to 0.36 mW per resistor.
The 100 kOhm pair also raises output resistance from 5 kOhm to 50 kOhm, so load resistance, leakage, and ADC sampling become more important.
Choosing practical resistor values
Start with the required ratio, then choose the resistor sum from current budget and output stiffness. Low-value dividers suit noisy or loaded nodes but waste power. High-value dividers suit low-power monitoring only when leakage, loading, tolerance, and acquisition time remain acceptable.
- Use the voltage divider calculator to check ratio, current, per-resistor power, tolerance, and preferred-value pairs.
- Use the loaded divider calculator when the receiving circuit input resistance is known.
- Use the resistor power calculator when divider current or voltage is high enough that package margin matters.
Power and package margin
Divider power is usually small, but low-value or high-voltage dividers can dissipate enough heat to need a real wattage check. Calculate each resistor power separately because the voltage drop is not always split evenly. Then apply margin, package derating, voltage rating, and pulse or transient checks where relevant.
Common mistakes
- Choosing the divider ratio but ignoring continuous current draw in battery or standby circuits.
- Choosing very high resistor values without checking load resistance, input leakage, contamination, or ADC acquisition time.
- Checking total divider current but not power in each individual resistor.
- Assuming a divider that is safe at room temperature still has margin in a hot enclosure or tiny package.
When the approximation breaks down
- The simple current and power equations assume a static unloaded divider. A finite load changes the effective lower resistance and the output voltage.
- ADC inputs, switched-capacitor sampling, fast enable pins, and noisy environments may need source-impedance limits or a buffer instead of only a DC divider calculation.
- High-voltage dividers need resistor voltage rating, creepage, clearance, and often multiple series parts even when power is low.
Further checks and references
- Check the next-stage input resistance, leakage, bias current, and sampling behaviour before relying on a high-value divider.
- Review resistor datasheet power derating and voltage rating when divider current, voltage, or ambient temperature is not trivial.
- For battery systems, include divider current in the sleep-current budget or switch the divider only when measurement is needed.
Related calculators
Voltage divider calculator
Calculate divider ratio, current, per-resistor power, tolerance, and preferred values.
Loaded voltage divider calculator
Check the output after the receiving circuit input resistance is connected.
Resistor power calculator
Apply wattage margin and review package-level power checks.