How do I convert MPa to psi?

Multiply MPa by 145.04. For example, a tensile strength of 50 MPa is about 7,250 psi. To go from psi to MPa, multiply by 0.006895.

How do I convert notched Izod from ft-lb/in to J/m?

Multiply ft-lb/in by 53.38 to get J/m. Results in kJ/m² come from the ISO test, which divides by area on a different specimen, so they cannot be converted to J/m with a factor.

Is specific gravity the same as density in g/cm³?

Almost. Specific gravity compares the resin with water and has no unit. At room temperature it differs from density in g/cm³ by well under one percent, which is close enough for part weight but not for a specification.

How do I convert g/cm³ to lb/in³?

Multiply g/cm³ by 0.036127. A resin at 1.20 g/cm³ is about 0.0434 lb/in³, or 74.9 lb/ft³.

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Plastics unit converter

Data sheet units, metric and U.S., converted as you type.

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Precision

Unit	Value	Copy

Part weight from volume

Part weight is volume times density. Pick a resin for a typical density, or type the density from your data sheet.

Part volume

Resin

Density (g/cm³)

Typical densities only. Fillers, color and grade change density, so use the figure on the data sheet for the grade you run. To turn part weight and monthly volume into gaylords and truckloads, use the order-size calculator.

Common data sheet conversions

Multiply the value in the first column by the factor to get the second unit.

From	To	Multiply by
MPa	psi	145.04
psi	MPa	0.006895
GPa (modulus)	ksi	145.04
g/cm³	lb/ft³	62.428
g/cm³	lb/in³	0.036127
in³/lb	cm³/g	0.036127
ft·lbf/in (notched Izod)	J/m	53.379
J/m	ft·lbf/in	0.018734
V/mil	kV/mm	0.03937
kV/mm	V/mil	25.4
W/(m·K)	BTU·in/(hr·ft²·°F)	6.9335
J/(g·K)	BTU/(lb·°F)	0.23885
µm/(m·°C)	µin/(in·°F)	0.5556
mil	mm	0.0254
lb/hr	kg/hr	0.45359
Pa·s	poise	10

Temperatures are not a simple multiplication: °F = °C × 1.8 + 32. Heat values use the International Table BTU and calorie.

Conversions that trip people up

Notched Izod in J/m and kJ/m² are different tests. J/m (ASTM D256) is energy per unit of notch width. kJ/m² (ISO 180) is energy per unit of cross-section area, on a different specimen. You cannot convert one to the other with a factor, so compare like with like.
Specific gravity is close to, not equal to, density in g/cm³. Specific gravity compares the resin with water, so it has no unit. At room temperature the two numbers differ by well under one percent, which is fine for part weight but not for a spec.
A temperature difference is not a temperature. A 10°C rise is an 18°F rise, not 50°F. For spreads, tolerances and set-point changes, pick Δ°C or Δ°F in the unit list.
HDT and Vicat need the load as well as the number. A heat deflection temperature at 0.45 MPa (66 psi) reads much higher than one at 1.8 MPa (264 psi) for the same resin.
Melt flow has no unit conversion. g/10 min only compares at the same temperature and load. See melt flow index explained.

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Matching a grade across data sheets

Send the data sheet for the resin you run, and a polymer chemist finds a matching grade and quotes it.

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