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Pressure and Force Unit Conversion

Guide · Updated October 28, 2026

Gauges, presses, material data and drawings mix inch and metric pressure units constantly. These factors come from the exact definitions used by NIST (Special Publication 811): 1 lbf = 4.4482216 N, 1 kgf = 9.80665 N exactly, 1 bar = 100,000 Pa exactly, 1 MPa = 1 N/mm², and 1 psi = 6,894.757 Pa. Because MPa is newtons per square millimeter, it is the natural metric unit for material strength, and 1 ksi (1,000 psi) is 6.894757 MPa.

Step by step

1. Identify both units: Check whether a gauge reads psi, bar or kPa, and whether it is gauge or absolute.
2. Pick the factor: Use the table, multiplying from the unit you have.
3. Multiply: For example 3,000 psi × 0.0689476 = 206.8 bar.
4. Sanity check: 1 bar is about 14.5 psi; 1 MPa is about 145 psi.
5. Convert force separately: Force = pressure × area; keep area units consistent.
6. Round at the end: Carry four significant figures through the math.

Pressure conversion factors

• 1 psi = 6.894757 kPa = 0.0689476 bar = 0.00689476 MPa
• 1 bar = 14.50377 psi = 100 kPa = 0.1 MPa
• 1 MPa = 145.0377 psi = 10 bar = 1 N/mm²
• 1 ksi = 1,000 psi = 6.894757 MPa
• 1 kgf/cm² = 14.22334 psi = 0.980665 bar
• 1 standard atmosphere = 14.69595 psi = 1.01325 bar = 101.325 kPa
• 1 in Hg (32 °F) = 0.491154 psi = 3.38639 kPa
• 1 in H2O (39.2 °F) = 0.036127 psi = 249.09 Pa

Force conversion factors

• 1 lbf = 4.448222 N = 0.4535924 kgf
• 1 N = 0.2248089 lbf = 0.1019716 kgf
• 1 kgf = 9.80665 N = 2.204623 lbf
• 1 kN = 224.8089 lbf
• 1 US ton-force (2,000 lbf) = 8.896443 kN = 907.18 kgf
• 1 metric tonne-force = 9.80665 kN = 2,204.6 lbf

Common shop values

• Shop air 90 psi = 6.21 bar = 0.621 MPa
• Hydraulic 3,000 psi = 206.8 bar = 20.68 MPa
• Hydraulic 5,000 psi = 344.7 bar
• Hydraulic 10,000 psi (portable rams) = 689.5 bar = 68.95 MPa
• Mild steel yield 36 ksi = 248.2 MPa
• Grade 8 bolt tensile 150 ksi = 1,034 MPa
• Class 10.9 bolt tensile 1,040 MPa = 150.8 ksi

The bolt grade comparisons are approximate matches only: SAE J429 Grade 8 is 150 ksi minimum tensile and ISO 898-1 class 10.9 is 1,040 MPa minimum; they are not interchangeable specifications.

Worked example: press tonnage from gauge

A hydraulic press has a 3.0 in bore cylinder and the gauge reads 4,000 psi. Area = π ÷ 4 × 3.0² = 7.069 in². Force = 4,000 × 7.069 = 28,274 lbf = 14.1 US tons. In metric, 28,274 × 4.448222 = 125.8 kN, or 12.83 tonne-force.

Worked example: metric data sheet

A data sheet lists 6061-T6 yield as 276 MPa. 276 × 145.0377 = 40,030 psi, or 40.0 ksi, which matches the commonly published 40 ksi minimum. A pump rated 250 bar is 250 × 14.50377 = 3,626 psi.

Common problems

Mixing gauge (psig) and absolute (psia) pressure, treating kgf/cm² as exactly 1 bar (it is 0.98 bar), forgetting that force depends on area, and using a press near its gauge limit. Gauges drift; have critical gauges calibrated on the same interval you use for gage blocks.

FAQ

How many psi in a bar?

14.50377 psi.

How do I convert MPa to psi?

Multiply by 145.0377.

How many newtons in a pound-force?

4.448222 N.

What is 1 ksi in MPa?

6.894757 MPa.

Is kgf/cm² the same as bar?

Close but not equal: 1 kgf/cm² = 0.980665 bar.

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General shop information only — follow your drawing, tool maker's data and your quality system.