Calculator
Enter up to six resistors. Leave unused resistor fields empty. Choose a known source value, then calculate drops, power, percentages, totals, and verification.
Example Data Table
This worked example uses a 12 V source with three series resistors: 100 Ω, 220 Ω, and 330 Ω.
| Item | Value |
|---|---|
| Total Resistance | 650 Ω |
| Circuit Current | 0.0185 A |
| Voltage Drop Across 100 Ω | 1.846 V |
| Voltage Drop Across 220 Ω | 4.062 V |
| Voltage Drop Across 330 Ω | 6.092 V |
| Sum of Drops | 12.000 V |
Formula Used
R_total = R1 + R2 + R3 + ...I = V_total / R_totalV_i = I × R_iV_i = V_total × (R_i / R_total)P_i = I² × R_iIn a series circuit, the same current flows through every resistor. The total resistance equals the sum of all resistors. If the source voltage is known, current comes from Ohm’s law. Each resistor drop is then current multiplied by that resistor.
If current is known instead, multiply current by total resistance to get total voltage. Voltage distribution follows the resistance ratio, so larger resistors take larger drops.
How to Use This Calculator
Frequently Asked Questions
1) What is voltage drop in a series circuit?
Voltage drop is the portion of source voltage appearing across each resistor. In series, the same current flows through every component, so larger resistance creates a larger drop.
2) Why do all voltage drops add up to the source voltage?
Kirchhoff’s Voltage Law states that the algebraic sum of voltages around a closed loop is zero. In a simple series loop, individual drops therefore add to the applied source voltage.
3) Does current change from one resistor to another in series?
No. In a series circuit there is only one current path. The exact same current passes through every resistor, lamp, or component connected in that single chain.
4) Can I calculate voltage drops without knowing current?
Yes. If total source voltage and all resistor values are known, find total resistance first, compute current using Ohm’s law, then determine each drop from that current or from resistance ratios.
5) What happens if one resistor is much larger than the others?
The largest resistor receives the largest share of the source voltage because voltage division in series is proportional to resistance. It may also dissipate significant power if current is high.
6) Why does this calculator show resistor power too?
Power helps you check safe component ratings. A resistor may have the correct resistance value but still fail if it must dissipate more heat than its wattage rating allows.
7) Can this calculator handle kilo-ohms and mega-ohms?
Yes. You can choose Ω, kΩ, or MΩ for resistor inputs. The calculator converts everything internally to ohms, then applies the same series formulas consistently.
8) When should I use the current-known mode?
Use current-known mode when current is measured directly or specified by design. The calculator then finds total source voltage and every resistor drop from that common current and the entered resistances.