Predict pressure changes in fixed-volume nitrogen systems based on temperature shifts (Amontons's Law).
PSI
Bar
kPa
Fahrenheit (°F)
Celsius (°C)
Calculated Result:
The predicted final pressure is:
*Calculation assumes a constant volume and dry nitrogen gas behavior.
Understanding Nitrogen Pressure and Temperature
Nitrogen is widely used in automotive, aerospace, and industrial applications because it is more stable than compressed air. However, nitrogen is still subject to the laws of physics—specifically the Ideal Gas Law. This calculator uses Gay-Lussac's Law (also known as Amontons's Law), which states that the pressure of a given mass of gas is directly proportional to its absolute temperature when the volume is kept constant.
The Formula for Pressure Change
To calculate how the pressure of nitrogen will change as temperature rises or falls, we use the following equation:
P₂ = P₁ × (T₂ / T₁)
P₁: Initial Pressure
T₁: Initial Absolute Temperature (in Kelvin)
P₂: Final Pressure
T₂: Final Absolute Temperature (in Kelvin)
Why Nitrogen is Used in Tires and HVAC
Nitrogen is preferred over regular air in high-performance environments for several reasons:
Moisture Control: Nitrogen is typically "dry," whereas compressed air contains water vapor. Water vapor causes more extreme pressure fluctuations during temperature changes.
Oxidation Reduction: Oxygen causes rubber and metal components to degrade over time. Nitrogen is inert and extends the life of internal components.
Consistent Pressure: While nitrogen still expands and contracts with heat, it does so more predictably than "wet" air.
Common Pressure Reference Table
Condition
Typical Temp (°F)
Pressure Change Trend
Cold Startup
32°F – 60°F
Baseline Pressure
Highway Driving
100°F – 130°F
~10-15% Increase
High-Performance Racing
160°F+
Significant Expansion
Practical Example
Imagine you fill your truck tires with nitrogen to 35 PSI at a garage temperature of 65°F. If you drive into a desert climate where the tire temperature reaches 115°F, what happens? Using the calculator, we convert the temperatures to Kelvin (291.48K and 319.26K). The result shows the pressure would increase to approximately 38.3 PSI.
function calculateNitrogenPressure() {
var p1 = parseFloat(document.getElementById("initialPressure").value);
var pUnit = document.getElementById("pressureUnit").value;
var t1 = parseFloat(document.getElementById("initialTemp").value);
var t2 = parseFloat(document.getElementById("finalTemp").value);
var tUnit = document.getElementById("tempUnit").value;
var resultBox = document.getElementById("resultBox");
var output = document.getElementById("pressureOutput");
if (isNaN(p1) || isNaN(t1) || isNaN(t2)) {
alert("Please enter valid numerical values for all fields.");
return;
}
var t1Kelvin, t2Kelvin;
// Convert Initial Temperature to Kelvin
if (tUnit === "F") {
t1Kelvin = (t1 – 32) * (5/9) + 273.15;
} else {
t1Kelvin = t1 + 273.15;
}
// Convert Final Temperature to Kelvin
if (tUnit === "F") {
t2Kelvin = (t2 – 32) * (5/9) + 273.15;
} else {
t2Kelvin = t2 + 273.15;
}
// Guard against absolute zero or negative temperatures
if (t1Kelvin <= 0 || t2Kelvin <= 0) {
alert("Temperature cannot be at or below absolute zero.");
return;
}
// Gay-Lussac's Law: P2 = P1 * (T2 / T1)
var p2 = p1 * (t2Kelvin / t1Kelvin);
// Format output
var formattedResult = p2.toFixed(2) + " " + pUnit;
output.innerHTML = formattedResult;
resultBox.style.display = "block";
}