Enter the resistance values to calculate the total equivalent resistance (Rtotal).
The total equivalent resistance is:
0 Ω
How to Calculate Resistors in Parallel
In a parallel circuit, electrical current has multiple paths to flow through. Adding more resistors in parallel actually reduces the total resistance of the circuit because you are providing more paths for the current to take.
To find the total resistance (Rtotal), you must first find the reciprocal of each individual resistor (1 divided by the resistance value). Sum these reciprocals together, and then take the reciprocal of that sum to get the final result.
Example Calculation:
If you have two resistors in parallel: R1 = 100Ω and R2 = 200Ω.
Step 1: 1 / 100 = 0.01
Step 2: 1 / 200 = 0.005
Step 3: 0.01 + 0.005 = 0.015
Step 4: 1 / 0.015 = 66.67Ω
Therefore, the total resistance is 66.67 Ohms.
Key Rules for Parallel Resistors
The Lower Bound Rule: The total resistance of a parallel circuit will always be less than the value of the smallest individual resistor.
Equal Resistors: If you have two resistors of the same value in parallel, the total resistance is exactly half of one resistor's value. For example, two 50Ω resistors in parallel result in 25Ω.
Current Distribution: In a parallel circuit, the voltage across each resistor is the same, but the current splits, with more current flowing through the path of least resistance.
function calculateParallelResistance() {
var r1 = document.getElementById('res1').value;
var r2 = document.getElementById('res2').value;
var r3 = document.getElementById('res3').value;
var r4 = document.getElementById('res4').value;
var inputs = [r1, r2, r3, r4];
var sumOfReciprocals = 0;
var activeCount = 0;
var isValid = true;
for (var i = 0; i < inputs.length; i++) {
var val = parseFloat(inputs[i]);
if (!isNaN(val) && val !== "") {
if (val <= 0) {
alert("Resistance values must be greater than zero.");
isValid = false;
break;
}
sumOfReciprocals += (1 / val);
activeCount++;
}
}
if (!isValid) return;
if (activeCount = 1000) {
displayVal = (totalResistance / 1000).toFixed(3) + " kΩ";
} else {
displayVal = displayVal + " Ω";
}
document.getElementById('total-r-display').innerText = displayVal;
document.getElementById('resistor-result').style.display = 'block';
document.getElementById('calc-summary').innerText = "Calculated using " + activeCount + " resistors in parallel.";
// Scroll to result
document.getElementById('resistor-result').scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}