Voltage Divider Calculator
Free Voltage divider Calculator for electrical projects. Enter dimensions to get material lists and cost estimates. Includes formulas and worked examples.
Calculator
Adjust values & calculateConnected between Vin and Vout
Connected between Vout and Ground
Formula
The voltage divider formula calculates the output voltage as a fraction of the input voltage based on the ratio of R2 to the total series resistance (R1 + R2). The current through the divider is determined by the total resistance. Power dissipation in each resistor equals IยฒR.
Last reviewed: December 2025
Worked Examples
Example 1: 5V to 3.3V Level Shifting
Example 2: Battery Voltage Monitoring
Background & Theory
The Voltage Divider Calculator applies the following established principles and formulas. Structural and construction engineering is governed by fundamental load analysis, material science, and regulatory standards that ensure the safety and durability of built structures. The primary distinction in load analysis is between dead loads โ the permanent self-weight of structural elements, finishes, and fixed equipment โ and live loads, which represent variable occupancy, furniture, and environmental forces such as wind and snow. These are combined using factored load equations, such as the ASCE 7 formula U = 1.2D + 1.6L, where D is dead load and L is live load. Concrete mix design is governed by the water-cement (w/c) ratio, which is the primary determinant of compressive strength and durability. A w/c ratio of 0.40โ0.45 typically yields concrete with 28-day compressive strengths of 30โ40 MPa. Common mix ratios by weight for structural concrete are approximately 1 part cement : 1.5โ2 parts sand : 3 parts coarse aggregate. Structural steel is characterized by its yield strength (the stress at which permanent deformation begins, typically 250โ350 MPa for mild steel) and ultimate tensile strength (typically 400โ500 MPa). Mid-span deflection of a simply supported beam under a central point load is given by ฮด = FLยณ / (48EI), where F is force, L is span length, E is Young's modulus, and I is the second moment of area. Building insulation is rated by R-value, a measure of thermal resistance in units of mยฒยทK/W (SI) or ftยฒยทยฐFยทh/BTU (imperial). Higher R-values indicate greater resistance to heat flow. Foundation design depends on the allowable bearing capacity of the underlying soil, which ranges from approximately 75 kPa for soft clay to over 10,000 kPa for bedrock. Drainage gradients for surface water are typically specified as a minimum of 1โ2% slope away from building foundations to prevent hydrostatic pressure and water infiltration.
History
The history behind the Voltage Divider Calculator traces back through the following developments. The history of construction engineering spans thousands of years of accumulated empirical knowledge and, more recently, rigorous scientific analysis. The ancient Egyptians built the Great Pyramid of Giza around 2560 BCE using an estimated 2.3 million stone blocks, demonstrating sophisticated logistics, geometry, and workforce organization. Roman engineers advanced the field dramatically through the use of pozzolanic concrete โ a mixture of volcanic ash, lime, and seawater โ enabling the construction of the Pantheon dome (43.3 m diameter, completed around 125 CE) and a vast network of aqueducts and roads across the empire. Cast iron emerged as a structural material during the Industrial Revolution, first used prominently in the Iron Bridge at Coalbrookdale, England, completed in 1779. Wrought iron and later steel allowed far greater spans and heights. The Eiffel Tower, completed in 1889, demonstrated the structural possibilities of wrought iron at scale and influenced the development of steel-frame skyscraper construction in Chicago and New York. Reinforced concrete was systematically developed by Joseph Monier, a French gardener, who patented iron-reinforced concrete pots and panels in the 1860s, and later by engineers including Franรงois Hennebique who created the first comprehensive reinforced concrete framing system in the 1890s. The 1906 San Francisco earthquake caused widespread devastation and galvanized the engineering profession to develop seismic design provisions. Subsequent earthquakes โ including the 1971 San Fernando and 1994 Northridge events โ drove successive improvements in seismic codes, base isolation technology, and ductile detailing of reinforced concrete and steel frames. Building codes became increasingly standardized in the twentieth century, with the International Building Code (IBC) first published in 2000 providing a unified model code adopted across much of the United States. Building Information Modeling (BIM) emerged in the 2000s as a digital workflow integrating architectural, structural, and MEP design into a unified three-dimensional model, fundamentally changing coordination practices across the industry.
Key Features
- Solve Ohm's law for any unknown (voltage, current, resistance, or power) given two known values, with a circuit diagram and power dissipation warning for component ratings.
- Decode 4-band and 5-band resistor color codes to resistance value and tolerance, or reverse-lookup the color bands for a given resistance.
- Calculate RC circuit charge and discharge time constants, showing the voltage at any time step and the time to reach common thresholds (63%, 99%).
- Compute LC resonance frequency from inductance and capacitance values, useful for filter design, oscillator circuits, and impedance matching.
- Determine op-amp gain (inverting and non-inverting configurations) and unity-gain bandwidth product from resistor values and datasheet GBW specifications.
- Size the current-limiting resistor for an LED from supply voltage, forward voltage, and desired forward current, with power dissipation and nearest standard resistor value.
- Calculate PCB trace width required to carry a specified current without exceeding temperature rise limits, following IPC-2221 internal and external layer standards.
- Compute transformer primary-to-secondary turns ratio, output voltage, output current, and VA rating from input specifications and winding parameters.
Frequently Asked Questions
Formula
Vout = Vin ร R2 / (R1 + R2) | I = Vin / (R1 + R2)
The voltage divider formula calculates the output voltage as a fraction of the input voltage based on the ratio of R2 to the total series resistance (R1 + R2). The current through the divider is determined by the total resistance. Power dissipation in each resistor equals IยฒR.
Worked Examples
Example 1: 5V to 3.3V Level Shifting
Problem: Design a voltage divider to convert a 5V signal to 3.3V for a microcontroller input.
Solution: Required ratio: 3.3/5 = 0.66\nChoose R2 = 20kฮฉ\nR1 = R2 ร (Vin/Vout - 1) = 20k ร (5/3.3 - 1) = 20k ร 0.515 = 10.3kฮฉ\nNearest standard: R1 = 10kฮฉ\nActual Vout = 5 ร 20k/(10k + 20k) = 3.33V\nCurrent: I = 5V / 30kฮฉ = 0.167mA
Result: R1 = 10kฮฉ | R2 = 20kฮฉ | Vout = 3.33V | I = 0.167mA
Example 2: Battery Voltage Monitoring
Problem: Monitor a 12V battery with a microcontroller ADC that has a 3.3V maximum input.
Solution: Required ratio: 3.3/12 = 0.275\nChoose R2 = 10kฮฉ\nR1 = R2 ร (Vin/Vout - 1) = 10k ร (12/3.3 - 1) = 10k ร 2.636 = 26.36kฮฉ\nNearest standard: R1 = 27kฮฉ\nActual Vout = 12 ร 10k/(27k + 10k) = 3.24V\nCurrent: I = 12V / 37kฮฉ = 0.324mA
Result: R1 = 27kฮฉ | R2 = 10kฮฉ | Vout = 3.24V | I = 0.324mA
Frequently Asked Questions
What is a voltage divider?
A voltage divider is a simple circuit that uses two resistors connected in series to produce an output voltage that is a fraction of the input voltage. The output voltage is taken across the second resistor (R2). Voltage dividers are one of the most fundamental and commonly used circuits in electronics, found in sensor interfaces, reference voltage generation, level shifting, volume controls, and biasing transistor circuits. The key formula is Vout = Vin x R2 / (R1 + R2).
How do I calculate voltage divider output?
The voltage divider formula is Vout = Vin x (R2 / (R1 + R2)). R1 is the resistor connected between the input voltage and the output node, and R2 is the resistor connected between the output node and ground. For example, with Vin = 12V, R1 = 10kohm, and R2 = 10kohm, Vout = 12 x (10000 / 20000) = 6V. The ratio R2/(R1+R2) is called the divider ratio and always falls between 0 and 1, meaning the output voltage is always less than or equal to the input voltage.
Why does loading affect voltage divider output?
When you connect a load (such as a circuit or component) to the output of a voltage divider, the load resistance appears in parallel with R2, effectively reducing the R2 value and lowering the output voltage. For the divider to work accurately, the load resistance should be at least 10 times greater than R2 (the 10x rule). For critical applications, use a buffer amplifier (op-amp voltage follower) between the divider output and the load to prevent loading effects.
Can a voltage divider be used as a power supply?
Voltage dividers should generally NOT be used as power supplies. They are designed for signal-level applications, not for delivering significant power. Problems include: poor voltage regulation (output voltage changes with load), wasted power (current flows through R1 and R2 even with no load), and inability to supply meaningful current without large voltage drops. For power supply applications, use voltage regulators (like LM7805), DC-DC converters, or switching regulators instead.
How do I choose resistor values for a voltage divider?
When choosing resistor values: (1) Calculate the required ratio: ratio = Vout/Vin = R2/(R1+R2). (2) Choose R2 first, typically between 1kohm and 100kohm for general use. (3) Calculate R1 = R2 x (Vin/Vout - 1). (4) Select the nearest standard resistor values. (5) Verify the current draw is acceptable: I = Vin/(R1+R2). Lower resistor values give better load regulation but waste more power. Higher values save power but are more sensitive to loading. A common guideline is to keep divider current at least 10x the expected load current.
How accurate are the results from Voltage Divider Calculator?
All calculations use established mathematical formulas and are performed with high-precision arithmetic. Results are accurate to the precision shown. For critical decisions in finance, medicine, or engineering, always verify results with a qualified professional.
References
Reviewed by Daniel Agrici, Founder & Lead Developer ยท Editorial policy