Convert a tensile or yield figure between MPa, N/mm², ksi and psi, and Charpy impact energy between joules and foot-pounds. For reading a drawing written in one unit system against a certificate written in another.
| N/mm² | ksi | psi |
|---|---|---|
| 400 | 58.0 | 58,015 |
| 500 | 72.5 | 72,519 |
| 550 | 79.8 | 79,771 |
| 600 | 87.0 | 87,023 |
| 650 | 94.3 | 94,275 |
| 700 | 101.5 | 101,526 |
| 750 | 108.8 | 108,778 |
| 800 | 116.0 | 116,030 |
| 850 | 123.3 | 123,282 |
| 900 | 130.5 | 130,534 |
| 1,000 | 145.0 | 145,038 |
| 1,100 | 159.5 | 159,542 |
| 1,200 | 174.0 | 174,045 |
| 1,500 | 217.6 | 217,557 |
| ksi | N/mm² | psi |
|---|---|---|
| 60 | 414 | 60,000 |
| 70 | 483 | 70,000 |
| 80 | 552 | 80,000 |
| 90 | 621 | 90,000 |
| 100 | 689 | 100,000 |
| 110 | 758 | 110,000 |
| 120 | 827 | 120,000 |
| 125 | 862 | 125,000 |
| 130 | 896 | 130,000 |
| 140 | 965 | 140,000 |
| 150 | 1,034 | 150,000 |
| 160 | 1,103 | 160,000 |
| 180 | 1,241 | 180,000 |
| 200 | 1,379 | 200,000 |
| Joules | ft·lb |
|---|---|
| 7 | 5.2 |
| 14 | 10.3 |
| 20 | 14.8 |
| 27 | 19.9 |
| 34 | 25.1 |
| 40 | 29.5 |
| 47 | 34.7 |
| 54 | 39.8 |
| 60 | 44.3 |
| 70 | 51.6 |
| 80 | 59.0 |
| 100 | 73.8 |
| 120 | 88.5 |
| 150 | 110.6 |
A pascal is one newton per square metre. A megapascal is a million of them. One newton per square millimetre is also a million newtons per square metre, because there are a million square millimetres in a square metre — so 1 N/mm² and 1 MPa are the same unit written two ways.
This matters because the two notations appear side by side in practice. A BS EN specification will give a minimum tensile in MPa, a mill certificate will print it in N/mm², and nothing has changed between them. If you find yourself reaching for a conversion factor between the two, there isn't one.
The conversion that does need care is into imperial. Strength in ksi and impact energy in foot-pounds use entirely different factors, because one is a stress and the other is an energy.
A mill certificate issued to BS EN 10204 reports the mechanical properties actually measured on the cast or the batch: tensile strength, yield or proof stress, elongation, and where the specification calls for it, Charpy impact energy at a stated temperature.
UK and European certificates state stress figures in N/mm² and impact energy in joules. A customer drawing written to a US standard will ask for ksi and foot-pounds. The certificate still satisfies the drawing — the numbers simply have to be put into the same units before they can be compared, which is the job this page does.
Watch the yield figure in particular: a specification may quote proof stress (Rp0.2) where the certificate reports upper yield (ReH), and those are different measurements, not different units. Converting one into ksi will not make it into the other. Parkside supplies EN 10204 3.1 certification on request — see accreditations and quality.
Parkside Steel (Stockholders) Ltd has supplied engineering steel bar since 1977. We stock bright drawn and black round bar, hexagon, square, flat bar and bright equal angle across the EN grades — EN1A, EN3B, EN8, EN8D, EN16, EN19, EN24, EN36, S355 J2 and more — plus grey and ductile cast iron bar.
Material certification to EN 10204 is available on request, and all stock can be cut to length on our 13 on-site saws, from 10mm to 600mm diameter. Call 01623 687 660 or email sales@parksidesteel.uk.com.
The questions engineers and buyers ask most often when a drawing and a certificate are written in different units.
Yes — they are identical, not approximately equal. One megapascal is one million pascals, and a pascal is one newton per square metre. One newton per square millimetre is therefore 106 N/m², which is exactly 1 MPa. A tensile strength of 850 N/mm² and one of 850 MPa are the same number describing the same thing, so no conversion is needed — only a change of notation.
Multiply by 6.894757. A specification calling for 120 ksi minimum tensile is asking for 827 N/mm². Going the other way, divide by the same figure: 850 N/mm² is 123.3 ksi. The converter above does this live in both directions.
A ksi is simply one thousand psi — the ‘k’ is kilo. Steel strength figures in psi run to six digits, so US drawings and ASTM specifications almost always use ksi instead. A 120 ksi tensile is 120,000 psi.
Multiply joules by 0.737562. The 27 J minimum that appears throughout European impact specifications is just under 20 ft·lb. Going the other way, multiply foot-pounds by 1.355818. Note that impact energy is a measure of absorbed energy, not stress, so it converts on a completely different factor from tensile and yield.
UK and European mill certificates issued to BS EN 10204 state tensile and yield in N/mm², and impact energy in joules at a stated test temperature. If your customer's drawing is written in ksi, the certificate still satisfies it — the figures simply need converting. Parkside supplies EN 10204 3.1 certification on request; see accreditations and quality.
No — this converter changes the units of a strength figure you already have. Deriving an approximate tensile strength from a hardness reading is a different calculation, and it is on the hardness conversion page, which converts between HRC, HB, HV and an estimated tensile in N/mm². Take the figure from there and bring it here to put it into ksi or psi.