What is the formula to tell how much cash is on had?

No Formulae Is Available To Know " How Much Is Equal To Cash In Hand "
But By Following General Practice Of Accounting And Auditing We Have Two Methods To Know The Amount Of Cash In Hand

1 To Count It Physically

Or

2 Try To Make Cash Flow Statement, Which Actually Tells U How Much Inflow
And Outflow Has Taken Place.

Cash Inflow - Cash Outflow = Cash In Hand

See Some Books Or Cash Flow Softwares Over Net

Hope This Helps U A Bit : )