Measure from the center of the rotor drive shaft to the bottom of the tube.
Relative Centrifugal Force0 x g
Understanding Centrifuge G-Force (RCF)
In laboratory settings, it is crucial to distinguish between RPM (Revolutions Per Minute) and RCF (Relative Centrifugal Force). While RPM measures how fast the rotor is spinning, RCF (measured in "g") describes the actual force exerted on the contents of the tubes. Because different centrifuges have different rotor sizes, spinning at the same RPM will yield different results on different machines.
The Mathematical Formula
The standard formula used by this calculator to convert RPM to G-force is:
RCF (g) = 1.118 × 10⁻⁵ × r × (RPM)²
r: The rotational radius in centimeters (cm).
RPM: Revolutions per minute.
1.118 × 10⁻⁵: A constant derived from the conversion of units.
Example Calculation
If you are using a rotor with a radius of 10 cm and you set the speed to 3,000 RPM:
Square the RPM: 3,000 × 3,000 = 9,000,000.
Multiply by the radius: 9,000,000 × 10 = 90,000,000.
Multiply by the constant: 90,000,000 × 0.00001118 = 1,006.2 x g.
Why the Radius Matters
The radius should be measured from the center of the spindle to the bottom of the centrifuge tube (R-max). If you measure to the top of the liquid (R-min), you will calculate the force at the surface, which is significantly lower. Most scientific protocols specify R-max values for sedimentation tasks.
function calculateGForce() {
var rpm = document.getElementById("rpmInput").value;
var radius = document.getElementById("radiusInput").value;
var resultDiv = document.getElementById("rcfResult");
var gValueDisplay = document.getElementById("gForceValue");
var adviceDisplay = document.getElementById("rcfAdvice");
if (rpm > 0 && radius > 0) {
// Formula: RCF = 0.00001118 * r * (RPM)^2
var rcf = 0.00001118 * parseFloat(radius) * Math.pow(parseFloat(rpm), 2);
// Round to 2 decimal places or whole number if large
var formattedRCF = rcf > 100 ? Math.round(rcf).toLocaleString() : rcf.toFixed(2);
gValueDisplay.innerText = formattedRCF + " x g";
resultDiv.style.display = "block";
// Add descriptive context based on force
if (rcf = 1000 && rcf < 15000) {
adviceDisplay.innerText = "Standard benchtop centrifuge range. Common for DNA extraction and clearing lysates.";
} else {
adviceDisplay.innerText = "High-speed/Ultracentrifugation range. Used for isolating organelles, viruses, or proteins.";
}
} else {
alert("Please enter valid positive numbers for both RPM and Radius.");
resultDiv.style.display = "none";
}
}