SIMPLE   LHC   LUMINOSITY   CALCULATOR

 INPUT: 
Bunch population N = protons   (or ions)
Colliding bunch pairs nbb = bunches
Number of bunches per beam kb = bunches
Revolution frequency frev = Hz
Beam energy E = TeV   (GeV used below)
Beta* β* = m
Normalised transverse emittance   εɴ= μm     (m used below)
Full crossing angle α = μrad   (stops parasitic collisions kb>154)
Bunch length (RMS) σz = cm     (or ns*30)   (m used below)
Process cross section σproc = mb     (10-27 cm2)   (10-31 m2)
Planned run time T = days   (or h/24 for hours)
Overall run factor H = %      (or 1 or less for factor, incl h/24)

 OUTPUT: 
Lorentz factor γ   =    γ = E / (0.938 GeV)
Transverse emittance ε   =   m ε = εɴ / γ
Transverse beam size at IP   σx = σy  =   μm σxσy = ε β*
Geometric factor S   =   S = (1 + (σz / σx)2 tan2(α/2))-1/2
Luminosity per bunch pair Lbb   =   Hz/cm2 Lbb = frev N2 S / (4π ε β*)
Average number of processes per crossing   μ   =   μ = σproc Lbb / frev
Luminosity (all bunches) L   =   Hz/cm2 L = nbb Lbb   (1/μb=1e+30/cm2, 1/nb=1e+33/cm2)
Integrated luminosity (per IP)Lint   =   Lint = L H T   (reality may be 25% less)
Rate of processes R   =   Hz R = L σproc
Stored beam energy Estored   =   MJ Estored = E N kb

Modified from http://lpc.web.cern.ch/lpc/lumi.html 2010-08-08, but layout left very similar for comparison.
Values updated 2011-04-17, but Transverse separation and Separation factor not added (default 0 and 1 anyway)