Resistance Calculator
Calculate total resistance for series and parallel resistor circuits. Add up to 8 resistors, get results in Ω, kΩ, and MΩ. Parallel mode also shows total conductance in Siemens.
Resistance Formulas
R_total = R₁ + R₂ + … + Rₙ
Total resistance equals the sum of all individual resistors. Current is the same through all.
1/R = 1/R₁ + 1/R₂ + … + 1/Rₙ
Reciprocal of total equals sum of reciprocals. Voltage is the same across all branches.
How to Use the Resistance Calculator
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1Choose Circuit TypeSelect Series for resistors connected end-to-end, or Parallel for resistors connected side-by-side.
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2Enter Resistor ValuesStart with 3 inputs. Click "+ Add Resistor" to include up to 8 resistors. Values are in Ohms.
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3Remove Unused InputsClick the × button next to any row to remove it. A minimum of 2 resistors is required.
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4View ResultsTotal resistance is shown in Ω, kΩ, and MΩ. Parallel mode also shows conductance in Siemens.
Example: 3 Resistors
Frequently Asked Questions
In a series circuit, resistors are connected end-to-end so the same current flows through all of them. The total resistance is the sum. In a parallel circuit, resistors share the same two nodes so the same voltage appears across each. The total resistance is always less than the smallest individual resistor.
Parallel resistors are used to decrease total resistance or to handle higher current/power. They are common in power distribution, current sensing, and load balancing. House wiring uses parallel circuits so each appliance gets the full supply voltage.
Conductance is the reciprocal of resistance: G = 1/R, measured in Siemens (S). It represents how easily current flows. In parallel circuits the total conductance is simply the sum of individual conductances: G_total = G₁ + G₂ + … + Gₙ.
Resistors are manufactured in standardized E-series values. The E12 series has 12 values per decade: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 (and multiples/fractions thereof). The E24 series has 24 values, and E96 has 96 values per decade for precision applications.
Adding any parallel path always gives current more routes to flow, increasing total current for the same voltage. By Ohm's Law (R = V/I), higher current means lower equivalent resistance. Even adding a very large resistor in parallel slightly lowers the total below the previous smallest value.
Related Calculators
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Watt Calculator
Calculate electrical power in watts from voltage and current, or resistance and voltage.