BYTETOOLS

Voltage Divider Calculator

Solve the voltage divider equation Vout = Vin·R2/(R1+R2) for output voltage or a missing resistor, with divider current, power and loaded-output mode.

6 V
Vout (unloaded)
3 mA
Divider current
9 mW
Power in R1
18 mW
Power in R2

Output voltage

Vout = 9 × 2 kΩ ÷ (1 kΩ + 2 kΩ). Divider current I = Vin ÷ (R1 + R2); power per resistor P = I²R.

What is the Voltage Divider Calculator?

The ByteTools Voltage Divider Calculator solves the two-resistor divider in every direction. Compute the output voltage from Vin, R1 and R2 with Vout = Vin × R2 ÷ (R1 + R2); or enter a target Vout and let the tool solve for the missing resistor.

  • Solves for Vout, R1 or R2
  • Loaded-output mode with RL in parallel with R2
  • Divider current and power dissipation per resistor
  • Unit prefixes for volts and ohms
  • Formula printed with your values substituted in
  • 100% private — runs entirely in your browser

How to use the Voltage Divider Calculator

  1. 1

    Choose what to solve for: Vout, R1 or R2.

  2. 2

    Enter the known values with their unit prefixes.

  3. 3

    Optionally enter a load resistance to see the loaded output voltage.

  4. 4

    Read Vout (or the missing resistor), divider current and per-resistor power.

  5. 5

    Copy the results with one click.

About the Voltage Divider Calculator

The ByteTools Voltage Divider Calculator solves the two-resistor divider in every direction. Compute the output voltage from Vin, R1 and R2 with Vout = Vin × R2 ÷ (R1 + R2); or enter a target Vout and let the tool solve for the missing resistor. It also reports the divider current and the power dissipated in each resistor.

A load-resistance mode models what really happens when you connect the divider to something: the load RL sits in parallel with R2, pulling the output below the unloaded value. This is the classic gotcha with dividers, and the calculator shows both the unloaded and loaded output side by side.

Everything is computed 100% locally in your browser — no uploads, no accounts, works offline. Ideal for sensor interfaces, reference voltages and level shifting.

Frequently asked questions

How does a voltage divider work?

Two resistors in series split the input voltage in proportion to their resistances. The output across R2 is Vout = Vin × R2 ÷ (R1 + R2). With Vin = 9 V, R1 = 1 kΩ and R2 = 2 kΩ, the output is 9 × 2000 ÷ 3000 = 6 V.

How do I choose resistor values for a divider?

The ratio sets the voltage; the absolute size sets the current. Smaller resistors waste more power but hold their voltage better under load; larger ones save power but are more easily disturbed. A common compromise is total resistance in the 10 kΩ–100 kΩ range for signal work.

Why does my divider voltage drop when I connect a load?

The load resistance sits in parallel with R2, lowering the effective bottom resistance and therefore Vout. A rule of thumb is to keep the load at least 10× larger than R2 so the droop stays under about 5%. The calculator's load mode shows the exact loaded voltage.

Can I use a voltage divider as a power supply?

Generally no. Dividers only hold their ratio for very light loads, and they continuously burn power in both resistors. For powering circuits, use a voltage regulator or DC-DC converter; use dividers for references, sensing and level shifting.

How much power do divider resistors dissipate?

The divider current is I = Vin ÷ (R1 + R2), and each resistor dissipates P = I² × R. For 9 V across 3 kΩ total, I = 3 mA, so R1 (1 kΩ) dissipates 9 mW and R2 (2 kΩ) 18 mW — negligible for standard 1/4 W parts.

Related tools