# Voltage Divider Calculator Free voltage divider calculator, also a resistor divider calculator. Enter Vin, R1 and R2 to get the output voltage, current and power — or set a target Vout and get the exact resistor values plus the nearest standard E-series resistors, with the real-world output error. Find your output voltage in seconds. Enter **Vin, R1 and R2** to get the divider output, current and power — or flip to **target-voltage mode** and get the exact resistor values plus the nearest standard **E-series resistors**. It is also a **resistor divider calculator**: the two names describe the same two-resistor circuit. Schematic diagram Results Output voltage — R1 — R2 — Divider current — Power (R1+R2) — A resistor divider is for sensing and reference levels, not for powering a load. Any current drawn from Vout pulls the voltage down — add a buffer or regulator if the load matters. ## Don't pick resistors by hand A calculator is great for a sanity check — but you still have to translate the numbers into real parts, drop two resistors on a schematic, wire the divider, and label the net. In Flux, you just ask. Flux picks the **E-series resistor pair**, places the divider, and wires it into your rail — live on the canvas. - Describe the rail, get real E-series parts — not just raw numbers - Flux places and wires the divider for you - Swap the target voltage and it re-picks the resistors instantly [Try Flux for Free](https://www.flux.ai/signup) ### In Flux Design a 5 V to 3.3 V voltage divider and place it on my schematic ![Flux](https://www.flux.ai/p/assets/site/6446c14683b3da60aea75bce_copilot-icon-filled-white.svg) Done! For a 5 V → 3.3 V divider I went with standard E24 resistors: - **R1 (top):** 1.0 kΩ - **R2 (bottom):** 2.0 kΩ That gives an output of **3.33 V** with a divider current of about **1.67 mA**. I've placed both resistors and wired the divider onto your schematic. Want me to try a different ratio or tolerance? ## How the voltage divider is calculated The divider ratio, currents and power are all computed client-side as you type. 01 ### Divider ratio The output is Vin scaled by the ratio of the bottom resistor R2 to the total resistance R1 + R2. 02 ### Solve for a resistor Fix R1 and a target Vout, and the exact R2 falls out. The calculator then snaps to the nearest E-series value. 03 ### Current & power Larger resistors waste less power but are noisier and sag more under load. Check the current and power before you commit. ## Resistor divider calculator Engineers call this circuit a resistor divider, a resistive divider or a voltage divider. The names are interchangeable, because the divider is built from two resistors and the output depends only on their ratio. Use the calculator above for either term. A resistor divider is the right tool for scaling a signal into an ADC, setting a comparator threshold, biasing a transistor, or making a reference level. It is the wrong tool for powering a rail: the output impedance is R1 ∥ R2, so a real load pulls the voltage down. Enter your load resistance in the optional field to see how far the output sags. ## Voltage divider and resistor divider calculator FAQ ### How do you calculate a voltage divider? A resistor voltage divider scales the input voltage by the ratio of the two resistors. Use **Vout = Vin · R2 / (R1 + R2)**, where R1 is the top resistor (between Vin and the output node) and R2 is the bottom resistor (between the output node and ground). For example, with Vin = 5 V, R1 = 1 kΩ and R2 = 2 kΩ, Vout = 5 · 2 / (1 + 2) = 3.33 V. This calculator does it as you type and also gives you the current and power. ### Is a resistor divider calculator the same as a voltage divider calculator? Yes. A resistor divider (also called a resistive divider) and a voltage divider are the same two-resistor circuit, so a resistor divider calculator and a voltage divider calculator do the same job. Both use **Vout = Vin · R2 / (R1 + R2)**. The name "resistor divider" points at the parts, and "voltage divider" points at the function. This tool covers both: enter R1 and R2 to get the output voltage, or enter a target voltage to get the resistor pair. ### What is the voltage divider formula? The output-voltage formula is **Vout = Vin · R2 / (R1 + R2)**. To go the other way and size a resistor for a target output, rearrange it to **R2 = R1 · Vout / (Vin − Vout)**. The current through the (unloaded) divider is I = Vin / (R1 + R2), and the power dissipated is P = I² · (R1 + R2) = Vin · I. ### How do I choose R1 and R2 for a voltage divider? Only the ratio R2 / (R1 + R2) sets the output voltage, so infinitely many pairs give the same Vout. Pick the absolute values to balance two things: smaller resistors draw more current and sag less under load but waste more power; larger resistors save power but are noisier and more sensitive to loading and input bias currents. A common sweet spot for logic-level sensing is tens of kΩ. Then snap both values to a standard E-series (E24 or E96) — this calculator shows the nearest standard pair and the resulting error automatically. ### How do I get 3.3 V from 5 V with a voltage divider? You need R2 / (R1 + R2) = 3.3 / 5 = 0.66, i.e. R1 : R2 ≈ 1 : 1.94. A clean E24 choice is R1 = 1 kΩ and R2 = 2 kΩ, which gives 3.33 V — close enough for level sensing. Note: a divider is fine for reading a 5 V signal into a 3.3 V ADC input, but it is NOT a way to power a 3.3 V device — for that you need an LDO or buck regulator. ### Why does my voltage divider output sag under load? The formula assumes nothing draws current from the output node. As soon as you connect a load resistance R\_L, it sits in parallel with R2, lowering the effective bottom resistance and pulling Vout down. The effect is small only when R\_L is much larger than R2 (rule of thumb: R\_L ≥ 10 × R2). Enter a load value in the optional field to see the loaded output. If the load is significant, buffer the divider with an op-amp or use a regulator. ### What are E12, E24, and E96 resistor values? E-series are the standard resistor values manufacturers actually stock, spaced logarithmically so each decade has a fixed set. E12 has 12 values per decade (±10% parts), E24 has 24 (±5%), and E96 has 96 (±1%). Because your exact calculated resistor rarely exists, you round to the nearest E-series value — that's why this tool shows both the ideal resistors and the nearest buildable E-series pair with the real-world output error. ### How much current does a voltage divider draw? The quiescent current through an unloaded divider is I = Vin / (R1 + R2). With Vin = 5 V and R1 + R2 = 3 kΩ, that's about 1.67 mA, dissipating roughly 8.3 mW. Increase the resistor values to cut this current for battery-powered designs — just watch out for noise and loading as the impedance rises. ### Can I use a voltage divider to power a circuit? No. A divider can only supply tiny currents before its output collapses, and its output impedance is roughly R1 ∥ R2, so any real load pulls the voltage down. Dividers are for reference voltages, biasing, and scaling signals into an ADC or comparator. To power a device at a lower voltage, use an LDO or switching regulator instead — in Flux you can ask for exactly that. ## Design the whole board with AI From reference levels to routed copper — let Flux pick your parts and wire them up. [Try Flux for Free](https://www.flux.ai/signup)