Series Resistor Calculator | Total Resistance & Voltage Drop
Calculate the total resistance of up to 10 resistors connected in series (R = R1+R2+...). Also shows the voltage drop across each resistor.
How to Use
- Enter resistor values (in Ω) in each field. Start with at least 2 resistors.
- Click 'Add Resistor' to add more (up to 10 total).
- Optionally enter the supply voltage to calculate current and voltage drops.
- Click 'Calculate' to see the total resistance.
- The voltage drop across each resistor is proportional to its resistance: V_n = Vtotal × R_n / R_total.
- Use the 'Remove' button to delete a resistor from the calculation.
About Series Resistors
Series Resistance Formula
In a series circuit, resistors are connected end-to-end so the same current flows through all of them. The total resistance is the arithmetic sum: R_total = R1 + R2 + R3 + ... + Rn. Unlike parallel circuits, series resistance always increases as more resistors are added. This is because each additional resistor is an additional obstacle to current flow in the single path.
Voltage Division in Series Circuits
In a series circuit with a fixed supply voltage, each resistor drops a voltage proportional to its resistance: V_n = V_supply × R_n / R_total. This is the basis of the voltage divider. The sum of all voltage drops equals the supply voltage (Kirchhoff's Voltage Law). Larger resistors drop more voltage; smaller ones drop less.
Current in Series Circuits
The same current flows through every component in a series circuit. If total resistance is R and supply is V, current I = V / R. This means if one component fails open (infinite resistance), the entire circuit stops working. This is why holiday lights wired in series all go dark when one bulb fails. Modern strings use shunt resistors or bypass mechanisms to avoid this.
Practical Uses of Series Resistors
Series resistors are used to: (1) limit current in LED circuits, (2) create voltage dividers with fixed ratios, (3) add impedance to dampen oscillations (snubbers), (4) measure current via voltage drop (current shunts), and (5) balance parallel-connected components. Precision resistors in series can achieve resistance values not available in standard E-series values.
Key Features
- Supports up to 10 resistors in a single calculation
- Calculates total resistance and per-resistor voltage drops
- Optional supply voltage input for current calculation
- Dynamically add or remove resistors
Common Applications
- Adding series resistors to achieve non-standard resistance values
- Designing current limiting circuits for LEDs and other devices
- Calculating voltage drops for circuit analysis
- Building resistor networks and attenuators
- Educational circuit analysis exercises