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Lets say you have to fix something that needs a 15 Ohm 3 Watt resistor replaced, so you look in your parts stock and only find a 22 Ohm 2 Watts what resistor would you need to go in parallel with it, and would the 2 watt power rating be all right, by putting the three values 15 (in box 1), 3 (in box 2), 22 (in box 3) in the calculator above and pressing the [Answer] button, you will find the 2 Watts is just a fraction under the limit, this is all right (but check anyway) , a 47 Ohm (in box 4), 1 Watt will be good resistor to use in parallel.
You could if you wish find the resistor values by the hard way.
1/Total Resistance = 1/first resistor in parallel + 1/second resistor in parallel + 1/third ..........
or,
1/Total Resistance = 1/r1 + 1/r2 + 1/r3 ........
So without the calculator above you need,
1/unknown resistor = 1/original resistor - 1/first choice resistor
If you just need to find the value of two resistors in parallel try,
Total Resistance = (r1 * r2)/(r1+r2)
By leaving the "original resistor" power as "0" (box 2) then the calculator above can be use to find the total resistance (box 1) from two known resistors in parallel (box 3 & 4).
"NaN" on the calculator means that it is Not a Number, like infinity.
TOLERANCE CODE:
A = ±0.05%, Gray.
B = ±0.1%, Voilet.
C = ±0.0.25%, Blue, 0.25pF.
D = ±0.5%, Green, 0.5pF.
E = ±1pF.
F = ±1%, Brown.
G = ±2%, Red.
J = ±5%, Gold.
K = ±10%, Silver.
L = ±15%
M = ±20%, (No color, resistor)
N = ±30%
From Eric.
Have a happy day (Somebody has too).
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