
Details

Voltage [V] 
The measure of the power differental between two points. It is the electromotive force. This is measured in volts [V]. 
Current Iintensity
[I] 
The flow of electric charge across a surface. This is measured in amps [A]. 
Power
[P] 
The rate of energy transfer. This is measured in ['watts'] [W]. 
Resistance
[R] 
The rate of energy transfer. This is measured in ohms [Ω]. 

Formulas

To find 
Known 
Formula 
Volts 
Amps [I]
Resistance Ω

V = I x R

Volts 
Watts [P]
Amps [I]

V = ^{P}⁄_{I}

Volts 
Watts [P]
Resistance Ω

√ P x R

Amps [I]

Volts
Resistance Ω

I = ^{V}⁄_{R}

Amps [I]

Watts [P]
Volts

I = ^{P}⁄_{ V}

Amps [I]

Watts [P]
Resistance Ω

I = √ ^{P}⁄_{R}

Watts [P]

Volts
Amps [I]

P = V x I 
Watts [P]

Volts
Resistance Ω

P = ^{V2}⁄_{R} 
Watts [P]

Amps [I]
Resistance Ω

P = I^{2} x R 
Resistance Ω

Volts
Amps [I]

R = ^{V}⁄_{I}

Resistance Ω 
Volts
Watts [P]

R = ^{V2}⁄_{P} 
Resistance Ω 
Watts [P]
Amps [I]

R = ^{P}⁄_{I2} 

Further reference:

Revision history:
 20201202 : v1.4  Updated code for PHP 8.0
 PHP Warning: Undefined variable $count
defined.
 PHP Warning: Undefined array key "volts"
predefined $out array.
 PHP Fatal error: Uncaught TypeError: round(): Argument #1 ($num) must be of type intfloat, string given
test is_numeric()
 20201201 : v1.3  Fixed input bug. Watts field name mangled. Fixed.
 20201025 : v1.2  Updated PHP, to correct for warnings for lazy coding
 "Use of undefined constant amps  assumed 'amps'"
 "syntax error, unexpected '' (T_ENCAPSED_AND_WHITESPACE),"
 20170729 : v1.1  Fixed pow bug. x^2 != x*x . Use pow(x, 2).
Added if ($debug == 1), and index output of which formula(s) were used, with actual values.
 20170728 : v1.0  Original work.

 