Calculate Standard Cubic Centimeters per Minute (SCCM) based on Pressure Decay.
cc (mL)
Liters
Cubic Inches (in³)
Cubic Feet (ft³)
Include part volume + tester lines + internal pneumatics.
psi
kPa
mbar
Pa
bar
inH2O
Seconds
Minutes
Milliseconds
Calculated Leak Rate0.00 sccm
Leak Rate (sccs)–
Leak Rate (mbar·l/s)–
Leak Rate (Pa·m³/s)–
Understanding CTS Leak Rate Calculations
In the field of industrial leak testing, particularly when using instruments from manufacturers like Cincinnati Test Systems (CTS), determining the precise leak rate is critical for quality assurance. The "CTS Leak Rate" generally refers to the calculation derived from a **Pressure Decay** test, which is the most common method for testing non-porous parts.
This calculator uses the ideal gas law principles to convert a measured pressure drop over time into a volumetric leak rate, typically expressed in standard cubic centimeters per minute (sccm).
The Leak Rate Formula
The fundamental formula used to calculate the leak rate ($Q$) based on pressure decay is:
Q = [V × ΔP] / [t × P_std]
Q: Leak Rate (sccm)
V: Total System Volume (Part + Internal Volume of Tester + Connections)
ΔP: Pressure Drop during the test phase (Start Pressure – End Pressure)
t: Time duration of the test
P_std: Standard Atmosphere Pressure (typically 14.696 psi or 101.325 kPa)
Why Volume Accuracy Matters
One common error in setting up CTS leak testers is neglecting the volume of the connection hoses and the internal pneumatics of the tester itself. The System Volume input in this calculator should represent the total volume of air being pressurized. If you only input the volume of the part being tested, the calculated leak rate will appear lower than it actually is, potentially allowing defective parts to pass inspection.
Common Leak Rate Units
While sccm is the industry standard for automotive and medical device testing, other units are frequently used depending on the region and sensitivity requirements:
sccs: Standard Cubic Centimeters per Second (1 sccs = 60 sccm).
mbar·l/s: Millibar Liters per Second, common in vacuum testing and helium mass spectrometry.
Pa·m³/s: Pascal Cubic Meters per Second, the SI unit for leak rate.
This tool automatically converts your pressure decay data into these standard metrics to assist engineers and quality technicians in verifying machine settings and validating test limits.
function calculateLeakRate() {
// 1. Get Inputs
var volumeInput = document.getElementById("systemVolume").value;
var pressureInput = document.getElementById("pressureDrop").value;
var timeInput = document.getElementById("testTime").value;
// 2. Validate Inputs
if (volumeInput === "" || pressureInput === "" || timeInput === "") {
alert("Please enter values for Volume, Pressure Drop, and Time.");
return;
}
var vol = parseFloat(volumeInput);
var press = parseFloat(pressureInput);
var time = parseFloat(timeInput);
if (vol <= 0 || press < 0 || time <= 0) {
alert("Please enter valid positive numbers.");
return;
}
// 3. Get Units
var volUnit = document.getElementById("volumeUnit").value;
var pressUnit = document.getElementById("pressureUnit").value;
var timeUnit = document.getElementById("timeUnit").value;
// 4. Normalize to Base Units
// Base: Volume = cc (mL), Pressure = Atmosphere (atm), Time = Minutes
// Convert Volume to cc
var volCC = 0;
if (volUnit === "cc") volCC = vol;
else if (volUnit === "liters") volCC = vol * 1000;
else if (volUnit === "cu_in") volCC = vol * 16.387064;
else if (volUnit === "cu_ft") volCC = vol * 28316.8466;
// Convert Pressure Drop to ATM
// Standard Atmosphere Reference: 14.6959 psi = 101.325 kPa = 1.01325 bar
var pressATM = 0;
if (pressUnit === "psi") pressATM = press / 14.6959;
else if (pressUnit === "kpa") pressATM = press / 101.325;
else if (pressUnit === "mbar") pressATM = press / 1013.25;
else if (pressUnit === "pa") pressATM = press / 101325;
else if (pressUnit === "bar") pressATM = press / 1.01325;
else if (pressUnit === "inh2o") pressATM = press / 406.782; // approx at 4°C
// Convert Time to Minutes
var timeMin = 0;
if (timeUnit === "minutes") timeMin = time;
else if (timeUnit === "seconds") timeMin = time / 60;
else if (timeUnit === "milliseconds") timeMin = time / 60000;
// 5. Calculate SCCM
// Formula: Leak Rate (sccm) = (Volume_cc * Drop_atm) / Time_min
// This derives from Ideal Gas Law assuming temperature is constant and standard reference is used.
var sccm = (volCC * pressATM) / timeMin;
// 6. Calculate Conversions
var sccs = sccm / 60;
// mbar·l/s
// 1 sccm = 0.0168875 mbar·l/s (approx)
// More precise: 1 sccm = (1013.25 mbar / 1 atm) * (1 L / 1000 cc) / 60 sec/min
// 1 sccm = 1013.25 / 60000 mbar·l/s = 0.0168875
var mbarls = sccm * 0.0168875;
// Pa·m³/s
// 1 sccm = 1.68875e-6 Pa·m³/s
var pam3s = sccm * 0.00000168875;
// 7. Display Results
document.getElementById("results-area").style.display = "block";
document.getElementById("resultSccm").innerHTML = sccm.toFixed(3) + " sccm";
document.getElementById("resultSccs").innerHTML = sccs.toFixed(4) + " sccs";
// Use scientific notation for very small numbers
document.getElementById("resultMbarLs").innerHTML = mbarls < 0.001 ? mbarls.toExponential(3) : mbarls.toFixed(5);
document.getElementById("resultPaM3s").innerHTML = pam3s.toExponential(3);
}