# Formula Page

On this page are listed Tesla coil formulas for a reference to those who prefer to make calculations on paper. Below is a table of formulas on this page.

 Ohm's Law Transformer Input and Output Capacitive Reactance Inductive Reactance Resonant Circuit Formula Spiral Coil Helical Coil Inverse Conical Coil Secondary Coil Dimensions Medhurst Toroid Capacitance Sphere Capacitance Plate Capacitors Leyden Jar Capacitors AC RMS/Peak Voltage Rotary Gap Firing Rotary Gap Electrode Speed Energy for L and C

### Ohm's Law

 E = IZ P = IE

E = volts
I = current in amps
Z = impedance or resistance in ohms
P = power in watts

### Transformer Input and Output

EPIP = ESIS

EP = primary voltage
IP = primary current in amps
ES = secondary voltage
IS = secondary current in amps

### Capacitive Reactance XC = capacitive reactance in ohms
F = frequency in hertz

### Inductive Reactance XL = inductive reactance in ohms
F = frequency in hertz
L = inductance in henrys

### Resonant Circuit Formula  F = frequency in hertz
L = inductance in henrys

### Spiral Coil Inductance L = inductance of coil in microhenrys (µH) R = average radius of the coil in inches N = number of turns W = width of the coil in inches ### Helical Coil Inductance L = inductance of coil in microhenrys (µH) N = number of turns R = radius of coil in inches (Measure from the center of the coil to the middle of the wire.) H = height of coil in inches ### Inverse Conical Coil Inductance L = inductance of coil in microhenrys (µH) L1 = helix factor L2 = spiral factor N = number of turns R = average radius of coil in inches H = effective height of the coil in inches W = effective width of the coil in inches X = rise angle of the coil in degrees ### Secondary Coil Dimensions T = AH L = length of wire in feet
D = outer diameter of coil form in inches
H = height of windings in inches
A = number of turns per inch
T = total number of turns
B = thickness of wire in inches

### Medhurst C = self capacitance in picofarads
R = radius of secondary coil in inches
L = length of secondary coil in inches

### Toroid Capacitance D1 = outside diameter of toroid in inches
D2 = diameter of cross section of toroid in inches
This equation courtesy Bert Pool.

### Sphere Capacitance ### Plate Capacitors K = dielectric constant
A = area of each plate in square inches
N = number of plates
D = distance between plates in inches (thickness of dielectric)

### Leyden Jar Capacitors K = dielectric constant
D = diameter of jar in inches
H = height of jar in inches
T = thickness of jar in inches

### AC RMS and Peak Voltage

ERMS = 0.7071·E P

ERMS = RMS voltage
EP = peak voltage

### Rotary Spark Gap Firings per Second F = firings per second (hertz)
R = motor RPM rating
E = number of rotary electrodes

### Rotary Spark Gap Electrode Speed S = electrode speed (MPH)
R = motor RPM rating
D = diameter of electrode placement circle (inches)

### Energy for L and C

 Capacitance Inductance J = 0.5 V2 C J = 0.5 I2 L

J = joules of energy stored
V = peak charge voltage
I = peak current