Regulator Heatsink Sizing Calculator
A linear voltage regulator turns the voltage it drops into heat, and that heat must escape fast enough to keep the silicon junction below its limit. This calculator finds the power a regulator dissipates from the input voltage, output voltage, and load current, then works out the largest heatsink thermal resistance that will hold the junction under your chosen maximum at a given ambient temperature. Enter the junction-to-case and case-to-sink resistances from the datasheet to get the required heatsink resistance in degrees Celsius per watt.
Heatsink sizing formula
Power Pd = (Vin - Vout) * Iload
Max total theta JA = (Tj_max - Tambient) / Pd
Max heatsink theta SA = theta JA - (theta JC + theta CS)
theta JC = junction-to-case, theta CS = case-to-sink (from datasheet)
If the required heatsink resistance is zero or negative, no heatsink can cope: reduce the voltage drop or current, or use a switching regulator.
Thermal design context
- Power dissipated is the voltage dropped times the current, all converted to heat.
- A smaller theta SA value means a larger, more effective heatsink.
- Junction-to-case and case-to-sink resistances come from the datasheet and mounting; supply them as inputs.
- Design below the rated maximum junction temperature for reliable, long life.
- Switching regulators avoid most of this heat and often need no heatsink at all.
Regulator heatsink: frequently asked questions
How much power does a linear regulator dissipate?
A linear regulator drops the difference between input and output voltage at the load current. Power dissipated equals (Vin minus Vout) times current, plus a small quiescent term you can usually ignore. For example, dropping 12 V to 5 V at 1 A dissipates 7 watts as heat.
How do I find the heatsink thermal resistance I need?
The total junction-to-ambient thermal resistance must keep the junction below its maximum. Required total is (Tj_max minus Tambient) divided by power. The heatsink resistance is that total minus the junction-to-case and case-to-sink resistances, which come from the device datasheet and the mounting method.
What junction temperature should I design for?
Most silicon regulators allow a maximum junction temperature of 125 C or 150 C, but designing close to the limit shortens life and risks thermal shutdown. A common practice is to target 100 to 110 C maximum. The exact maximum is on the device datasheet, so it is a user input here.
What is a negative or n/a heatsink result telling me?
If the required heatsink thermal resistance comes out near zero or negative, no practical heatsink can keep the junction cool enough. That means you must reduce the input-to-output voltage drop, lower the current, or switch to a switching regulator, which wastes far less power.
Why are switching regulators more efficient?
A linear regulator burns the voltage difference as heat, so efficiency falls as the drop grows. A switching regulator transfers energy in pulses and can reach 85 to 95 percent efficiency regardless of the voltage difference, producing far less heat and often needing no heatsink.
Official sources
- Texas Instruments: linear regulator and thermal design documentation.
- NIST: thermal metrology and SI units.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.