Free Online Calculators

Electrical Calculators

4 free electrical calculators for Ohm's Law, LED resistor sizing, wire gauge selection, and battery runtime estimation. Instant results, no signup required.

⚡ Ohm's Law Calculator Calculate voltage, current, resistance, and power instantly. Enter any 2 values to get the other 2. Electrical 💡 LED Resistor Calculator Calculate the correct resistor for any LED circuit with E24 standard value and color code. Electrical 🔌 Wire Gauge Calculator Find the correct AWG wire gauge with voltage drop, power loss, and NEC ampacity ratings. Electrical 🔋 Battery Life Calculator Calculate battery runtime from capacity and current draw. Supports duty cycle and battery comparisons. Electrical

Understand and Design Electrical Circuits with Free Online Calculators

Whether you are a hobbyist wiring your first Arduino project, an automotive enthusiast upgrading your vehicle's electrical system, or a student learning circuit theory, having reliable electrical calculators at hand saves time and prevents mistakes. ThisCalc offers four free electrical calculators that cover the core calculations every electronics and electrical enthusiast needs - from the fundamental relationship between voltage, current, and resistance to battery sizing for remote-deployed sensors.

Ohm's Law - The Foundation of Electrical Engineering

Every electrical circuit, from a simple LED to a complex motor controller, is governed by Ohm's Law: V = IR. Voltage (V) in volts equals current (I) in amperes multiplied by resistance (R) in ohms. A fourth quantity, power (P = VI = I-R = V^2/R), ties energy consumption into the same framework. Our Ohm's Law calculator accepts any two of the four quantities - voltage, current, resistance, or power - and instantly solves for the remaining two. This makes it invaluable for tasks like sizing a power supply, calculating the heat dissipation of a resistor, or verifying that a component's current rating will not be exceeded.

For example, if you know a motor draws 2.5 A at 12 V, the calculator immediately tells you the effective resistance is 4.8 O and power consumption is 30 W. That 30 W figure is what you need to select an appropriately rated fuse and wire gauge - both of which flow naturally into the other calculators below.

LED Resistor Sizing - Getting the Current Right

LEDs are current-controlled devices - too little current and they are dim, too much and they fail. The correct current-limiting resistor is found with R = (Vs - Vf) / If, where Vs is your supply voltage, Vf is the LED's forward voltage, and If is the target forward current. The challenge is that standard resistors come in the E24 series (5% tolerance) and a mathematically perfect value like 147 O does not exist in a parts bin.

Our LED resistor calculator handles the full workflow: enter your supply voltage, LED color (which sets a typical Vf), and desired current, and it returns the exact calculated resistance, the nearest E24 standard value, the actual current through the LED with that standard resistor, and the resistor's color code bands. This is especially useful when building multi-LED circuits or converting an existing design to a different supply voltage.

Wire Gauge Selection - Safety and Efficiency

Undersized wire is one of the most common causes of electrical fires in DIY automotive and home projects. The right wire gauge depends on both ampacity (the maximum safe continuous current) and voltage drop (the resistance-induced voltage loss over distance). The two requirements can pull in opposite directions: a very long low-voltage run may need heavier wire to limit voltage drop even though ampacity alone would permit a thinner gauge.

Our wire gauge calculator takes your load current, one-way wire length, system voltage, and acceptable voltage drop percentage, then recommends the minimum AWG size that satisfies both constraints. It shows the NEC-rated ampacity for that gauge in standard installation conditions, the calculated voltage drop in both volts and percentage, and the resistive power loss in watts - useful for estimating efficiency losses in automotive wiring harnesses, solar panel runs, or low-voltage landscape lighting.

Battery Life Estimation - Runtime for Any Load

Battery-powered projects live or die by runtime calculations done before the first prototype is assembled. The basic formula is straightforward: Runtime (hours) = Capacity (mAh) / Average Current (mA). In practice, devices rarely draw steady current - a microcontroller might sleep at 10 microamps and wake briefly at 50 mA. The duty-cycle model accounts for this: effective average current equals peak current multiplied by the fraction of time the device is active.

Our battery life calculator supports both continuous-draw and duty-cycle scenarios. Enter your battery capacity in mAh, the current draw (or peak current and on-time percentage), and optionally a Peukert exponent for battery chemistry (lithium, lead-acid, NiMH each have different discharge characteristics). The calculator outputs runtime in hours and minutes and supports comparing multiple battery sizes side by side so you can find the lightest option that meets your runtime target.

Privacy and Accuracy

All four electrical calculators run entirely in your browser. No data is transmitted to any server and no account is required. The formulas used are standard electrical engineering equations: Ohm's Law, the LED resistor formula, AWG resistance tables from the NEC, and the Peukert battery model. Results are for design guidance and educational use - for safety-critical or high-voltage work, always consult a licensed electrician and follow applicable electrical codes.

Frequently Asked Questions

What is Ohm's Law?

Ohm's Law states that the voltage across a conductor is directly proportional to the current flowing through it, given by V = IR, where V is voltage in volts, I is current in amperes, and R is resistance in ohms. A fourth related quantity - power - is calculated as P = VI or P = I-R. Our Ohm's Law calculator lets you enter any two values to instantly solve for the other two, making it useful for circuit design, troubleshooting, and education.

How do I calculate the correct LED resistor value?

The formula for an LED current-limiting resistor is R = (Vs - Vf) / If, where Vs is the supply voltage, Vf is the LED forward voltage (typically 1.8-3.4 V depending on color), and If is the desired forward current (typically 10-20 mA). Our LED resistor calculator computes the exact value and then rounds to the nearest E24 standard resistor value, showing the resistor color code so you can identify the correct component from your parts bin.

What wire gauge do I need for my circuit?

Wire gauge selection depends on three factors: the current the wire must carry (ampacity), the acceptable voltage drop over the wire length, and the installation environment (conduit, free air, bundled). Our wire gauge calculator takes your current, wire length, voltage, and acceptable voltage drop percentage, then recommends the correct AWG size along with the NEC ampacity rating, calculated voltage drop, and power loss. For home wiring, always follow local electrical codes and consult a licensed electrician.

How do I calculate battery life?

Battery runtime is estimated by dividing the battery capacity in milliamp-hours (mAh) by the average current draw in milliamps (mA): Runtime (hours) = Capacity (mAh) / Current (mA). For devices with intermittent operation (duty cycle), the effective current is the peak current multiplied by the on-time fraction. Our battery life calculator handles both continuous and duty-cycle scenarios and supports comparing multiple battery chemistries side by side.

Are these electrical calculators accurate?

Yes. Each calculator uses standard electrical engineering formulas derived from Ohm's Law, Kirchhoff's laws, and NEC ampacity tables. Results are for design guidance and educational purposes. For safety-critical wiring, high-voltage systems, or commercial electrical work, always consult a licensed electrician and comply with applicable electrical codes. All calculations run entirely in your browser - no data is sent to any server.