Pounds Per Square Inch Interactive Calculator

Specifying hydraulic cylinders, pneumatic actuators, or pressure vessels usually means you’ll see PSI on one drawing, bar on the supplier’s sheet, and pascals in simulation output. If you get the unit conversion wrong, it leads to parts not matching up or, in the worst case, failure in the field. This PSI conversion calculator lets you find equivalent values across pascals, bar, atmospheres, and torr from a single value. It’s a practical tool for keeping hydraulic and pneumatic specs straight, especially when you’re working with both imperial and metric data. You’ll also find the relevant formulas, a worked compressor example, a direct rundown on absolute vs. gauge pressure, and a detailed FAQ.

What is PSI (pounds per square inch)?

PSI is a standard pressure unit in the imperial system. It tells you how much force is applied to every square inch of surface. With a higher PSI, there’s more force pushing on each inch—whether that’s air in a tire, oil in a hydraulic line, or gas in a pressure tank.

Simple Explanation

PSI is best understood mechanically: it’s just force divided by area. Try this—press your thumb on a table. Press harder, more pressure. Or press with the tip of a pen (less area), same force—pressure shoots up. Different industries use other pressure units—bar, pascal, atmosphere—but it’s all just variations on the same basic calculation. This calculator quickly converts between them so you’re less likely to mix things up when working from different sources.

📐 Browse all 1000+ Interactive Calculators

Visual Reference Diagram

How to Use This Calculator

1. Select the unit you want to convert from in the dropdown (like PSI to Bar, or Pascal to PSI).
2. Enter your pressure value in the provided field (the input will change based on the conversion mode).
3. The results panel will show your input converted into all the other main pressure units at once.
4. Click Calculate to get your results.

PSI Conversion Calculator

<> Embed this calculator → <> Embed this animation calculator →

Conversion Equations

If you want to convert PSI to another pressure unit, start with these formulas for quick calculation (the calculator on this page does all of this instantly).

Simple Example

Goal: Convert 100 PSI to all common pressure units.

• Input: 100 PSI
• Pascal: 100 × 6894.757 = 689,475.7 Pa
• Bar: 100 / 14.50377 = 6.895 bar
• Atmosphere: 100 / 14.69595 = 6.805 atm
• Torr: 100 × 51.71493 = 5,171.5 torr

Theory & Practical Applications

Fundamental Pressure Definitions and the PSI System

PSI measures how much force you’re putting on each square inch. One PSI is one pound-force spread over an inch squared. This sounds straightforward, but mistakes often come from the details: Absolute pressure (PSIA) counts total pressure (including atmospheric), while gauge pressure (PSIG) measures above atmospheric only. For example, a tire at 32 PSIG actually sits at about 46.7 PSIA at sea level. If you take the same tire to 5,000 feet elevation, where the air pressure drops to about 12.2 PSIA, now the absolute pressure in the tire is only 44.2 PSIA—even though your gauge still says 32.

The conversion number 6894.757 Pa per PSI comes from dividing one pound-force (4.448222 N) by one square inch (0.00064516 m²). For mental math, 6895 is often used, but that's off by 0.0035%. This level of error appears small but can matter in calibration labs or multi-stage calculations. For most field work, 6895 is usually “good enough”; for lab work or instrument settings, use the full figure. The pascal (newton per square meter) lines up well with SI mechanical calculations; PSI needs you to convert both force and area.

Unit System Interoperability in Engineering Practice

Most engineering teams have to deal with a mix of unit systems, which opens the door for mistakes that range from annoying to catastrophic. Everyone remembers the Mars Climate Orbiter, but plenty of shop-floor errors come from the same kind of problem—just less dramatic. You might get a European pneumatic cylinder rated at 10 bar (which is about 145 PSI), but someone treating bar as if it’s 10 PSI ends up running it way beyond spec. Say a European hydraulic cylinder is rated for 210 bar—that’s 3046 PSI. If you misread that as 2100 PSI (using a 10:1 conversion), you risk blowing out seals or worse.

The “atmosphere” unit (14.69595 PSI at sea level) changes with weather and altitude, but it’s common to forget that. This shows up in vacuum systems: “28 inches Hg vacuum” at sea level is about 13.75 PSIA absolute, but “14 PSI vacuum” could mean only 0.70 PSIA. At high altitudes, vacuum systems just can’t pull as low due to reduced atmospheric pressure. For example, at Denver’s elevation, a vacuum pump that achieves 29.5 inches Hg at sea level tops out at only 27.2 inches Hg—short of full vacuum—unless you rework your targets or system.

Pressure Measurement Instrumentation and Calibration

Bourdon tube gauges—common in industry—often drift with temperature, showing errors of 0.5-2% across their range. A gauge calibrated at 68°F might read 98 when you’ve really got 100 PSI at 200°F. Digital sensors are better—0.25% FS isn’t uncommon—but pay attention to whether they use atmospheric reference (vented) or a sealed factory reference (sealed gauge). With sealed references, going from sea level to altitude can shift the baseline by as much as a PSI. Pressure standards in a calibration lab use deadweight testers: known weights on a known piston area, adjusted for local gravity, air buoyancy, and fluid columns. Electronic secondaries maintain traceability but add uncertainty. For accurate calibration, you need to check across several points, not just one—hysteresis and non-linearity matter.

Industrial Applications Across Pressure Ranges

Tire pressure is a simple example everyone knows. Most cars run around 28-35 PSI; let pressure drop 5 PSI and rolling resistance goes up, fuel economy drops, and tire life suffers. Race tires go much higher—50-70 PSI when cold, sometimes up to 100 during racing. This reduces flex and keeps the car stable, but comfort and tire life don’t matter here. Aircraft tires hit 190-210 PSI, sometimes over 320 PSI for fighters. Failures at those pressures are violent, so inflation equipment and handling procedures must be strict.

Hydraulics run much higher—construction cylinders usually work at 3000-5000 PSI. For example, a 2” bore cylinder at 5000 PSI puts out over 15,700 pounds of force. Waterjets make these pressures look low; 60,000-90,000 PSI is standard for cutting, requiring specialized tubing and pumps. At these levels, even water isn’t “incompressible”—it compresses by about 4% at 60,000 PSI. You need to watch for delays in system response and account for viscosity increases when sizing components.

Vacuum work goes in the other direction. HVAC evacuation goes down to about 500-1000 microns (about 0.01 PSIA). Electron microscopes and chip fabs reach 10⁻⁸ torr, sometimes much lower. When you have to convert between torr, PSIA, and pascal for ultra-high vacuum specs, check every step—small math errors matter when figures are several decimal places apart. “Leak rates” are in torr-liters/sec but often must be turned into PSIG rates for system checks.

Worked Example: Multi-Stage Compressor System Analysis

Problem: Take a three-stage compressor working at 1,247 meters elevation (atmospheric pressure is 87,423 Pa). Stage 1 compresses to 3.72 bar, stage 2 to 18.34 bar, both with intercoolers back down to 38°C. Find all pressures in PSIA, PSIG, and bar. Calculate the pressure ratios, check if they’re balanced, and check safety factors on the discharge end.

Solution:

Step 1: Atmospheric pressure
Atmospheric pressure = 87,423 Pa.
Convert Pa to PSI: 87,423 / 6894.757 ≈ 12.68 PSIA.
This is a lot lower than sea level’s 14.696 PSIA.

Step 2: Stage 1
Inlet: 12.68 PSIA.
Outlet: 3.72 bar = 3.72 × 14.50377 = 53.95 PSIA.
Ratio: 53.95 / 12.68 = 4.254.
Gauge reading: 53.95 - 12.68 = 41.27 PSIG.

Step 3: Stage 2
Inlet: 53.95 PSIA.
Outlet: 18.34 bar = 18.34 × 14.50377 = 266.00 PSIA.
Ratio: 266.00 / 53.95 = 4.930.
Gauge: 266.00 - 12.68 = 253.32 PSIG.

Step 4: Stage 3 (balance check)
To get equal ratios, average r₁ and r₂: (4.254 + 4.930) / 2 = 4.592.
So: Stage 3 discharge = 266.00 × 4.592 = 1,221.47 PSIA.
Bar: 1,221.47 / 14.50377 = 84.21 bar.
Gauge: 1,221.47 - 12.68 = 1,208.79 PSIG.

Step 5: Whole system
Total pressure ratio: 1,221.47 / 12.68 = 96.33.
Ideal stage ratio: ∛96.33 = 4.584.
Check against actual: r₁ = 4.254 (7.2% low), r₂ = 4.930 (7.5% high), r₃ = 4.592 (right on).

Step 6: Efficiency check
Stage 1 does less work than ideal; stage 2 does more. Power requirement is about 2% higher than if the stages matched. Stage 2’s discharge runs hotter, so watch for temperature-driven derating.

Step 7: Safety factor
Discharge: 1,221.47 PSIA (84.21 bar). If piping is rated to 100 bar (1,450 PSI): 1,450 / 1,221.47 = 1.19 safety factor. That just covers the usual compressed air minimum, but it’s tight. Relief valve should open at about 90-93 bar (1,305-1,350 PSI) to give margin.

Critical Considerations for System Design

Using the wrong pressure units on a component spec isn’t just a math problem—it can get expensive quickly or worse. For example, a cylinder rated at 250 bar is built for 3,625 PSI. Mixing this up with 250 PSI means you buy much heavier hardware than you need. Doing it the other way—putting a 250 PSI part in a 250 bar system—leads straight to failure. Always confirm the rating units and clarify “bar” versus “PSI” before making sourcing decisions.

Temperature directly affects closed-system pressure. For example, if you charge a hydraulic accumulator to 3,000 PSI at 70°F and it warms to 120°F, pressure climbs to approximately 3,240 PSI assuming no volume change. Make sure relief valves are set based on the worst-case combination of temperature and pressure, not just pump output. For cryogenic work, temperature swings can drive pressures orders of magnitude above design, especially if venting is blocked or restricted.

Frequently Asked Questions