Enter your supply voltage and up to four resistor values, then choose series or parallel circuit configuration. The Power Dissipation Calculator returns the equivalent resistance, total current, and power dissipated by each resistor — plus a breakdown chart showing how power is distributed across the circuit.
Total Power Dissipated
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Equivalent Resistance
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Total Current
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Power in R1
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Power in R2
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Power in R3
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Power in R4
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Power dissipation is the process by which an electrical component converts electrical energy into heat. When current flows through a resistor, the resistor opposes the flow, and the energy lost appears as heat. It is measured in watts (W).
Power dissipation can be calculated using three equivalent formulas: P = VI (power equals voltage times current), P = I²R (power equals current squared times resistance), and P = V²/R (power equals voltage squared divided by resistance). All three give the same result when the correct values are used.
In a series circuit, the same current flows through every resistor. First calculate the equivalent resistance by summing all resistors: R_eq = R1 + R2 + ... Then find total current I = V / R_eq. The power in each resistor is P = I² × R, and total power is P_total = V × I.
In a parallel circuit, the same voltage appears across every resistor. Calculate the equivalent resistance using 1/R_eq = 1/R1 + 1/R2 + ... The power in each individual resistor is P = V² / R, and total power equals the sum of all individual powers.
A parallel circuit dissipates more total power than a series circuit with the same resistors and supply voltage. This is because a parallel circuit has a lower equivalent resistance, which allows more total current to flow from the source, resulting in higher total power.
In a series circuit, the resistor with the highest resistance value dissipates the most power, since the current is the same through all resistors and P = I²R. In a parallel circuit, the resistor with the lowest resistance dissipates the most power, since P = V²/R and the voltage is equal across all branches.
The heat dissipated by a resistor equals its power consumption in watts. Over time, the energy dissipated as heat is E = P × t (joules), where t is time in seconds. For thermal management, the junction temperature can be estimated using T_junction = T_case + (Rth × P_dissipated), where Rth is the thermal resistance.
A resistor's power rating (in watts) is the maximum power it can safely dissipate without overheating or failing. If the calculated power dissipation exceeds the rated value, the resistor may burn out. Always choose a resistor with a power rating at least 25–50% higher than the expected dissipation for a safety margin.