kPa to bar - Pneumatic Tool and Cylinder Pressures

Catalogue Says 620 kPa, the Regulator Reads Bar

Pneumatic component data is written in kilopascals. Cylinder force tables, valve flow figures, minimum pilot pressures, air-consumption ratings — all in kPa, because that is the SI unit the standards are drafted in. Then you walk out to the machine and every gauge on the filter-regulator-lubricator unit is graduated in bar. One number, two scales, and the arithmetic between them is the easiest in the whole pressure family.

Divide kPa by 100 — or multiply by 0.01 — because one bar is exactly 100 000 Pa. The 620 kPa an impact wrench is rated at is 6.2 bar, which is the mark you set on the regulator and, not coincidentally, the 90 psi the same tool would be labelled with in a US catalogue.

Where the Two Scales Collide on a Shop Floor

Datasheet against dial

Component catalogues quote kPa, while regulators, receivers and line gauges are almost universally marked in bar. Every commissioning job crosses the boundary at least once.

Force tables

Cylinder thrust is published at a nominal pressure, usually 600 kPa. Set the circuit at 5 bar instead of 6 and every figure in that column drops by a sixth.

Two gauges, two answers

The receiver gauge and the gauge after the FRL rarely agree. Filters, fittings and hose all take their cut, and tool ratings refer to pressure at the inlet while running.

Consumption ratings

Air demand is published in normal litres per minute at a stated pressure. Change the pressure and the flow figure no longer applies, so the two are always quoted as a pair.

From Catalogue Page to Regulator Knob

Four steps that cover most of what a pneumatics job needs, whether you are sizing a new circuit or working out why an existing tool is under-performing.

Enter the rated pressure from the datasheet

Type the kPa figure into the left box — 600, 620, 1000 — and the bar equivalent lands as you type. Decimal commas from a European datasheet are accepted, and spaces inside a number are ignored.

Set the regulator to the bar figure

Adjust with the tool running, not idle, because a dial that reads 6.2 bar at rest can sag well below it under demand. If it will not hold, the restriction is upstream — filter element, undersized hose or a quick coupler.

Take the number into your force calculation

Each field has a copy button that hands over the digits alone, so the value drops cleanly into a spreadsheet computing thrust or air demand. Ctrl + C inside a field behaves the same way.

Read a gauge back into datasheet units

Measured 5.5 bar at the tool inlet and want to compare it with the rating? The swap arrows (↔) reverse the pair; going that way the multiplier is 100, so 5.5 bar is 550 kPa against a 620 kPa specification — an 11 % shortfall that shows up directly in torque.

A maximum rating is not a set point. A cylinder rated 1000 kPa (10 bar) is meant to be worked well below that. Common practice is to run components at roughly 70–80 % of their maximum so seals, cushions and rod bearings see a sane duty.

Working Pressures Across a Compressed-Air System

Typical requirements for the components on a shop air circuit, in the kilopascals catalogues publish and the bar your gauges are graduated in.

Component or tool	Pressure (kPa)	Pressure (bar)	Where it is measured
Compressor receiver, cut-out	800	8.00	Tank gauge, upstream of everything
ISO cylinder, nominal rating	600	6.00	The pressure catalogue force tables assume
ISO cylinder, maximum rating	1 000	10.00	Structural limit, never a set point
1/2 in impact wrench	620	6.20	At the tool inlet, while running
Air ratchet or die grinder	620	6.20	At the tool inlet, while running
Framing nailer	480–830	4.80–8.30	Regulator, adjusted for fastener and material
Brad nailer or stapler	480–690	4.80–6.90	Regulator, lower end for softwood
Venturi vacuum generator	450	4.50	Supply port; more pressure does not mean more vacuum
Spray gun inlet	200	2.00	Gun handle gauge, with the trigger pulled
Pilot-operated valve, minimum pilot	150	1.50	Pilot port; below this the spool will not shift reliably

Turning Pressure into Thrust

Force is pressure times piston area, and it is worth doing in SI: 600 kPa is 0.6 N/mm², so a 50 mm bore with an area of 1 963 mm² pushes about 1 178 N. A 63 mm bore gives roughly 1 870 N and an 80 mm bore about 3 016 N at the same 6 bar. Subtract the rod area when the cylinder is retracting, and leave headroom for seal friction.

Run a bore range in one sitting

Because both boxes stay editable, you can convert a whole column of catalogue pressures one after another without clearing the field between entries.

Gauge reading back to spec units

The swap arrows turn a bar measurement taken at the FRL into the kilopascals the component was specified in, which is the comparison that actually settles an argument.

Imported tools in psi, and N/mm² for force work

Both unit lists carry all 26 pressure units in searchable groups, so a psi-rated import or an N/mm² figure for a thrust calculation is one selection away.

Decimals where a set point needs them

Results carry up to eight decimals with thousands spaced for readability, and copying strips units and spacing so the value pastes straight into a calculation.

Compressed-Air Circuit Questions

Why does nearly every shop settle on about 6 bar?

It is the point where tool design and running cost meet. Hand tools have been built around roughly 620 kPa for decades, cylinder catalogues publish their force columns at 600 kPa, and compressing air past that costs disproportionately more energy for little extra work. Compressors are usually set to cut out around 800 kPa (8 bar) so the receiver holds a buffer, and the FRL then knocks the line down to the working figure.

My cylinder is 500 N short of the catalogue figure. Where did the force go?

Check the pressure at the cylinder port while it is moving, not on the tank gauge. Catalogue thrust assumes the nominal pressure, typically 600 kPa, right at the piston. Drop to 5 bar (500 kPa) and a 63 mm bore falls from about 1 870 N to roughly 1 558 N. On the retract stroke the rod area is subtracted, so pull force is always lower than push, and seal friction takes a further few percent.

Should the regulator be set to the pressure the tool is rated at?

Set it so the tool sees its rated pressure with the trigger held, which usually means dialling the regulator slightly higher than the target. A regulator holds its set point at low flow and droops under demand, so an idle reading of 6.2 bar can collapse to 5 bar the moment an impact wrench spins up. Adjust while the tool runs, and if the gauge will not hold, look at the filter element and the couplers before touching the knob again.

How much pressure does a long hose actually cost me?

More than most people expect, and it depends on flow far more than length. A generous 10 mm hose feeding a modest tool may lose only 20–30 kPa (0.2–0.3 bar) over 10 m, while a narrow 6 mm coil hose feeding a high-consumption grinder can shed several hundred kilopascals — a whole bar or more. Quick-release couplers are often the worst single restriction in the run. If the tool underperforms only at the end of the reel, the hose is the suspect, not the compressor.

What does an air consumption figure in NL/min really mean?

Normal litres per minute counts the air after it has expanded back to reference conditions, so it is comparable between components regardless of the pressure they run at. That is why a consumption figure is always published alongside a pressure — a rating of 200 NL/min at 620 kPa says nothing useful if you run the tool at 400 kPa instead. Size the compressor on the sum of the NL/min figures for whatever runs at the same time, with margin, rather than on the number of outlets.

Kilopascals to Bar