TI Voltage Divider Calculator: Resistor Values and Output

A TI voltage divider calculator helps you find the output voltage from two resistors in series, or choose resistor values for a desired output. Enter the input voltage, the two resistor values, and—when checking a real circuit—the load resistance; the calculator below returns the unloaded output and the loaded output.

Formula

For an unloaded divider, the output is the input voltage multiplied by the lower resistor divided by the sum of both resistors:

V_out = V_in × R₂ / (R₁ + R₂)

Here, V_in is the supply or signal voltage in volts (V), V_out is the voltage measured across the lower resistor, R₁ is the upper resistor between input and output, and R₂ is the lower resistor between output and ground. Resistance is entered in ohms (Ω). The two resistors must be connected in series across the same input and ground reference.

A connected load changes the effective lower resistance. The calculator treats the load R_L as parallel with R₂: R_effective = R₂ × R_L / (R₂ + R_L). The loaded output is then V_in × R_effective / (R₁ + R_effective). The additional results show divider current, V_in / (R₁ + R₂), and total resistor dissipation without a load, V_in² / (R₁ + R₂). Current is displayed in milliamps (mA), and power in milliwatts (mW).

Worked Example

With the default values, V_in = 5 V, R₁ = 10,000 Ω, R₂ = 10,000 Ω, and R_L = 1,000,000,000 Ω:

1. Find the loaded lower resistance: 10,000 × 1,000,000,000 / (10,000 + 1,000,000,000) ≈ 9,999.9 Ω.
2. Calculate loaded output: 5 × 9,999.9 / (10,000 + 9,999.9) ≈ 2.500 V.
3. For the unloaded result, 5 × 10,000 / (10,000 + 10,000) = 2.500 V.
4. Unloaded current is 5 / 20,000 × 1,000 = 0.250 mA. Total unloaded divider power is 5² / 20,000 × 1,000 = 1.250 mW.

The enormous default load resistance approximates an open circuit, so the loaded and unloaded outputs agree to the displayed precision.

When to Use a Voltage Divider

Use a divider to produce a lower voltage from a known input when the output draws little current. It is commonly useful for setting a reference level, scaling a signal for a measurement input, or biasing a circuit. A passive divider does not regulate voltage: changes in its input or load can change its output.

To choose a resistor ratio for a target output, rearrange the unloaded equation: R₂ / R₁ = V_out / (V_in − V_out). For example, a target of half the input calls for equal resistors. This ratio sets the ideal voltage, but the absolute resistance values determine current consumption and how strongly the divider can drive a load. The calculator checks values you provide; it does not select a complete design or account for every component limitation.

Loading, Current, and Resistor Choice

The load resistance appears in parallel with R₂, reducing the effective lower resistance. That pulls the output below the unloaded calculation. A useful rule of thumb is to make the load resistance much larger than R₂; a ratio of ten to one limits the simple loading effect, but the acceptable error depends on the application. If the load varies or draws appreciable current, calculate the loaded output rather than relying on the ideal ratio.

• Higher resistor values reduce divider current and wasted power, but make the output more vulnerable to loading and electrical noise.
• Lower values make the divider stiffer, but draw more current and dissipate more power.
• Use the power result to understand ideal divider dissipation; check each resistor’s individual dissipation and rated limits for an actual circuit.
• Real resistors have tolerances, and input voltage can vary. These affect the output beyond the rounded calculator result.

Common Mistakes and Limits

R₁ is the resistor from the input to the output node; R₂ runs from that node to ground. Reversing their positions changes the ratio. Also distinguish the output voltage from the voltage dropped across a resistor: the output is measured across R₂, not R₁.

Enter both resistances in ohms. For example, 10 kΩ is 10,000 Ω; entering 10 instead would mean 10 Ω. The units must also match: do not enter millivolts as though they were volts. Results are rounded to three decimal places, so a displayed value is not a guarantee of that exact accuracy in a physical circuit.

The loaded calculation models a fixed resistive load connected from output to ground. It does not model an active input’s changing current, frequency response, resistor tolerance, temperature effects, or noise. An input with very high impedance may be approximated by a large R_L; for a circuit that needs a stable voltage under varying load, a buffer or voltage regulator may be more suitable.

Frequently Asked Questions

What is a TI voltage divider calculator?
It is a tool for calculating the output of a two-resistor divider, with “TI” commonly referring to Texas Instruments. The equations are standard circuit formulas and do not depend on a particular manufacturer.

How do I calculate a voltage divider by hand?
For a lightly loaded divider, multiply the input voltage by R₂ and divide by R₁ + R₂. If a load is connected across R₂, first replace R₂ with its parallel combination with the load resistance.

Why is my measured output lower than the calculated voltage?
A connected circuit may draw current and load the divider. Resistor tolerances, a lower-than-expected supply voltage, wiring errors, or measuring against the wrong ground reference can also explain a difference.

Can a voltage divider power a device?
Usually it is best for signals or references that draw little current. A device’s changing current can shift the output substantially; use a suitable regulator or buffer when the load needs a stable supply.

Does a voltage divider reduce current?
It draws current through its resistor chain, while the output current available to a load depends on the resistor values and loading. It is not a current regulator, and the voltage and current must be evaluated together for the intended circuit.

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in vin | Input voltage | V | 5 | 0 | 1000000
in r1 | Upper resistor | ohm | 10000 | 0.000001 | 1000000000000
in r2 | Lower resistor | ohm | 10000 | 0.000001 | 1000000000000
in rl | Load resistance | ohm | 1000000000 | 0.000001 | 1000000000000
out vout | Loaded output voltage | V | vin * (r2 * rl / (r2 + rl)) / (r1 + r2 * rl / (r2 + rl)) | 3
out vopen | Unloaded output voltage | V | vin * r2 / (r1 + r2) | 3
out current | Divider current without load | mA | vin / (r1 + r2) * 1000 | 3
out power | Divider resistor power total without load | mW | vin ^ 2 / (r1 + r2) * 1000 | 3