How this instrument works
Pascals are what you get when SI declines to invent a new unit: one newton over one square metre, kg·m⁻¹·s⁻² once you spell it out in base quantities. Left unprefixed it becomes currency for quiet pressures. Acousticians reference every decibel to 20 µPa and calibrate microphones at 1 Pa. Ventilation engineers balance ducts near 250 Pa, cleanroom cascades hold 12.5 Pa from room to corridor, and airtightness crews depressurise whole houses to 50 Pa. Push any of those through to pounds per square inch and you get a decimal with three or four leading zeros, which says a good deal about how differently these two units are sized.
This page's multiplier answers one narrow question: how hard does a single pascal push on a single square inch? A square inch spans 0.00064516 m², an inch having been exactly 25.4 mm since standards bodies on both sides of the Atlantic settled it in 1959, so one pascal lays 0.00064516 N across that area. Weigh those newtons in pounds — one avoirdupois pound is 0.45359237 kg, and under conventional gravity — 9.80665 m/s², a CGPM decision dating from 1901 — it pushes with 4.4482216152605 N — and your quotient is 0.0001450377377302092… lbf. Both terms are exact decimals, so their ratio is rational; it simply repeats instead of terminating, and this sheet keeps fourteen places of it.
Watch what each system does when its numbers turn awkward. SI keeps pascals and swaps prefixes: hectopascals across an isobar map, kilopascals in a water main, megapascals on a steel certificate, gigapascals for bulk modulus. Imperial practice swaps units instead. Pounds per square inch own middle ground — shop air at 90, hydraulic rams at 3000 — but below roughly one psi, tradesmen hand off to inches of water column for ductwork and inches of mercury for vacuum, while wind loading moves to pounds per square foot, one of which is 47.880259 Pa. Raw pascal figures often need converting for exactly that reason: they can be perfectly ordinary in their own system and still land where psi was never graduated.
- Enter your reading in the Pascals (Pa) field; it opens at 100000 Pa, where our worked example below begins.
- The PSI (psi) row carries your answer, refreshed on every digit you type.
- Holding kilopascals, bar or megapascals? Scale up first — multiply by 1000, 100000 and 1000000 respectively.
- Reading a manometer in inches of water column? One inch at 39.2 °F is 249.082 Pa.
- To run this conversion backwards, multiply your psi figure by 6894.757293168361.
Worked example — a raw pascal log on a psi-marked rig
A test rig sits 100000 Pa above ambient while its datalogger writes that pressure channel in raw pascals, no prefix, exactly as its SI tag was configured. Your relief valve and manifold dial are both American and both graduated in psi. Put 100000 into the Pascals (Pa) field and the PSI (psi) row returns 14.503773773 — call it 14.5 psi differential.
Those digits also tell you what your rig is holding. A psi being one pound-force per square inch, 14.503773773 psi means 14.5 pounds bearing on every square inch of loaded surface, so an 8 by 10 inch inspection cover on that vessel's flank carries 80 × 14.503773773 = 1160 pounds of net thrust. Eight bolts share it at 145 pounds apiece — worth knowing before anyone reaches for a spanner.
Questions
Is 0.00014503773773 rounded, and does it matter?
Rounded, and no. One pascal on one square inch is 0.00064516 N, a pound-force is 4.4482216152605 N, and their quotient reads 0.0001450377377302092151… — rational, since both terms are exact decimals, but repeating rather than terminating. Stopping at fourteen decimal places leaves answers low by 2.09 × 10⁻¹⁶ psi for each pascal you enter, an error that first surfaces twelve significant figures into your result. Deadweight testers, our most accurate pressure standards in routine service, are quoted to parts per million.
Why does my answer have so many leading zeros?
Because one pascal is close to seven thousand times smaller than one psi, so anything quoted in bare pascals converts to a fraction of a pound per square inch. A 50 Pa envelope test is 0.00725 psi; a 12.5 Pa cleanroom cascade is 0.0018 psi. Practitioners avoid working that way: American low-pressure trades reach for inches of water column, where 1 inH₂O is 249.082 Pa or 0.0361 psi, so 250 Pa of duct static reads as a hair over one inch. Four leading zeros usually mean inches of water is what your reader expects.
How do pascals connect to decibels and microphone ratings?
Sound pressure is measured in pascals, and decibels are simply a logarithm built on them. Zero dB SPL is defined as 20 µPa, near to what a healthy young ear can just detect, and that comes to 2.9 × 10⁻⁹ psi. One pascal works out to 94 dB, which is why acoustic calibrators put out exactly that level, and why capsule sensitivity gets printed in millivolts per pascal — around 50 mV/Pa for a half-inch measurement microphone. Nobody has ever rated a microphone in millivolts per psi.
What does 50 Pa mean on a blower-door report?
It is what airtightness testing runs at, in European and North American methods alike, and it converts to 0.00725 psi. Fifty pascals is genuinely feeble — roughly what a 30 km/h breeze presses onto a flat wall. Severity is not what matters; repeatability is. Leakage climbs with pressure, so every dwelling has to be depressurised to one agreed figure before air-change results from different houses mean anything side by side.
Should my reading be gauge, absolute or differential?
Whichever it already was — multiplying rescales a magnitude and cannot shift a zero point. That question bites harder here than on most pressure pages, because bare pascal figures usually arrive from ventilation, filtration and envelope work, where your quantity is a difference across something rather than a height above vacuum. Imperial practice marks that case psid, alongside psig for gauge and psia for absolute, whereas an SI reading often turns up as a bare number, leaving you to remember what it was measured against.
Which pound is hiding inside a psi?
Pound-force, never pound-mass. One psi is what an avoirdupois pound weighs when it rests on a square inch, and weight needs an acceleration attached: that conventional 9.80665 m/s² adopted in 1901, a representative value for sea level around 45° latitude. Because it is a convention rather than a local measurement, this conversion never varies. A gauge showing 14.5 psi in Quito, in Reykjavík or on Mars reports that same 100000 Pa; only what a mass genuinely weighs follows local gravity.