System of Units
The program accepts any consistent set of engineering units. Examples of consistent sets of units for basic parameters are shown in the tables below. The user should use great care when converting from one system of units to another. An excellent reference on the subject of units and conversion between the imperial and SI systems can be found in [JPT1977]. The program does not perform conversions.
Mechanical Analysis
Table 1: System of Units  Mechanical Parameters
Property 
SI 
Imperial 
Length 
m 
m 
m 
cm 
ft 
in 
Density 
kg/m^{3} 
10^{3} kg/m^{3} 
10^{6} kg/m^{3} 
10^{6} g/cm^{3} 
slugs/ft^{3} 
snails/in^{3} 
Force 
N 
kN 
MN 
Mdynes 
lb_{f} 
lb_{f} 
Stress 
Pa 
kPa 
MPa 
bar 
lb_{f} /ft^{2} 
psi 
Gravity 
m/sec^{2} 
m/sec^{2} 
m/sec^{2} 
cm/sec^{2} 
ft/sec^{2} 
in/sec^{2} 
Ball stiffness 
N/m 
kN/m 
MN/m 
Mdynes/cm 
lb_{f}/ft 
lb_{f}/in 
where: 
1 bar 
= 10^{6} dynes/cm^{2} = 10^{5} N/m^{2} = 10^{5} Pa ; 

1 atm 
= 1.013 bars = 14.7 psi = 2116 lb_{f}/ft^{2} = 1.01325 \(\times\) 10^{5} Pa ; 

1 slug 
= 1 lb_{f}sec^{2} /ft = 14.59 kg ; 

1 snail 
= 1 lb_{f}sec^{2} /in ; and 

1 gravity 
= 9.81 m/sec^{2} = 981 cm/sec^{2} = 32.17 ft/sec^{2} 
this bit from flac3d not in pfc.
One exception to the conversion rule above: for quantities representing angles, conversions are performed in FLAC3D.
Angles are always entered on the command line (and in the user interface) in degrees, though they may be stored and used in radians. The exception is FISH, which (like most programming languages) assumes all angle values are in radians.
Thermal Analysis
All thermal quantities must be given in a consistent system of units.
No conversions are performed by the program. The tables below present examples of consistent sets of units for thermal parameters.
Table 3: System of SI units for thermal problems
Property 
Units 



Length 
m 
m 
m 
cm 
Density 
kg/m^{3} 
10^{3} kg/m^{3} 
10^{6} kg/m^{3} 
10^{6} g/cm^{3} 
Stress 
Pa 
kPa 
MPa 
bar 
Temperature 
K 
K 
K 
K 
Time 
s 
s 
s 
s 
Specific Heat 
J/(kg K) 
10^{3} J/(kg K) 
10^{6} J/(kg K) 
10^{6} cal/(g K) 
Thermal Conductivity 
(W/mK) 
(W/mK) 
(W/mK) 
(cal/s)/cm^{2} K^{4} 
Convective HeatTrans. Coefficient 
(W/m^{2} K) 
(W/m^{2} K) 
(W/m^{2} K) 
(cal/s)/(cm^{2} K) 
Radiative HeatTrans. Coefficient 
(W/m^{2} K^{4}) 
(W/m^{2} K^{4}) 
(W/m^{2} K^{4}) 
(cal/s)/cm^{2} K^{4} 
Flux Strength 
W/m^{2} 
W/m^{2} 
W/m^{2} 
(cal/s)/cm^{2} 
Source Strength 
W/m^{3} 
W/m^{3} 
W/m^{3} 
(cal/s)/cm^{3} 
Decay Constant 
s^{1} 
s^{1} 
s^{1} 
s^{1} 
Table 4: System of imperial units for thermal problems
Property 
Units 

Length 
ft 
in 
Density 
slugs/ft^{3} 
snails/in^{3} 
Stress 
lb_{f} 
psi 
Temperature 
R 
R 
Time 
hr 
hr 
Specific Heat 
(32.17)^{1} Btu/(lb R) 
(32.17)^{1} Btu/(lb R) 
Thermal Conductivity 
(Btu/hr)/(ft R) 
(Btu/hr)/(in R) 
Convective HeatTrans. Coefficient 
(Btu/hr)/(ft^{2} R) 
(Btu/hr)/(in^{2} R) 
Radiative HeatTrans. Coefficient 
(Btu/hr)/(ft^{2} R^{4}) 
(Btu/hr)/(in^{2} R^{4}) 
Flux Strength 
(Btu/hr)/ft^{2} 
(Btu/hr)/in^{2} 
Source Strength 
(Btu/hr)/ft^{3} 
(Btu/hr)/in^{3} 
Decay Constant 
hr^{1} 
hr^{1} 
where: 
1K 
= 1.8 R; 

1J 
= 0.239 cal = 9.48 × 10^{4} Btu; 

1J/kg K 
= 2.39 × 10^{4} btu/lb R; 

1W 
= 1 J/s = 0.239 cal/s = 3.412 Btu/hr; 

1W/m K 
= 0.578 Btu/(ft/hr R); and 

1W/m^{2} K 
= 0.176 Btu/ft^{2} hr R. 
Note that temperatures may be quoted in the more common units of °C (instead of K) or °F (instead of R),
where: 
Temp(°C) 
= [Temp(°F)  32]×(5/9); 

Temp(°F) 
= [1.8 Temp(°C) + 32]; 

Temp(°C) 
= Temp(K)  273; and 

Temp(°F) 
= Temp(R)  460. 
Fluid Analysis
Any set of units can be used as long as they are consistent with the units used in the mechanical calculation.
Table 7: System of SI units for fluid flow
Property 
Unit 
Symbol 
Length 
m 
l 
Fluid Density 
kg/m^{3} 
\(\rho_f\) 
Time 
s 
t 
Fluid Velocity 
m/s 
\(\vec{v}\) 
Particle Velocity 
m/s 
\(\vec{u}\) 
Porosity 

\(\epsilon\) 
Dynamic Viscosity 
Pa·s 
\(\mu\) 
Drag Coefficient 

\(C_d\) 
Reynolds Number 

\(Re\) 
Fluid Pressure 
Pa 
p 
Fluid Pressure Gradient 
Pa/m 
\(\vec{\nabla}p\) 
Fluid Kinematic Pressure 
m^{2}/s ^{2} 
P 
Kinematic Viscosity 
m^{2}/s 
\(\nu\) 
Structural Elements
Property 
Unit 
SI 
Imperial 
area 
length^{2} 
m^{2} 
m^{2} 
m^{2} 
cm^{2} 
ft^{2} 
in^{2} 
axial or shear stiffness 
force/disp 
N/m 
kN/m 
MN/m 
Mdynes/cm 
lb_{f} /ft 
lb_{f}/in 
exposed perimeter 
length 
m 
m 
m 
cm 
ft 
in 
moment of inertia 
length^{4} 
m^{4} 
m^{4} 
m^{4} 
cm^{4} 
ft^{4} 
in^{4} 
plastic moment 
forcelength 
Nm 
kNm 
MNm 
Mdynescm 
ftlb_{f} 
inlb_{f} 
yield strength 
force 
N 
kN 
MN 
Mdynes 
lb_{f} 
lb_{f} 
Young’s modulus 
stress 
Pa 
kPa 
MPa 
bar 
lb_{f} /ft^{2} 
psi 
where, 1 bar = 10^{6} dynes/cm^{2} = 10^{5} N/m^{2} = 10^{5} Pa.
Reference
[JPT1977]  Journal of Petroleum Technology. “The SI Metric System of Units and SPE’s Tentative Metric Standard”, 15751616 (December 1977). 