The current rating is not the thermal answer

Linear Regulator Thermal Calculator

Estimate the heat created by a linear regulator, the resulting junction temperature, and whether the input still clears the required dropout at your chosen operating point.

Put your board in the equation

Thermal and dropout estimate

Input voltageVUse the worst-case regulator-pin voltage, after upstream drops.Output voltageVUse the regulated rail target.Load currentmAUse the sustained load state you are checking.Ground / quiescent currentmATake this from the exact datasheet condition or bound.Required dropoutVUse the datasheet maximum at the relevant load and temperature when available.Local ambient°CEstimate the air or board environment around the regulator.Junction-to-ambient θJA°C/WUse the package/board value that matches your copper and airflow.Junction limit°CUse the applicable operating limit, not automatically the absolute maximum.

What the calculator does

Load dissipation: (VIN − VOUT) × ILOAD
Ground-current dissipation: VIN × IGND
Estimated junction: ambient + total dissipation × θJA
Electrical headroom: VIN − VOUT − required dropout

The model is deliberately simple. It does not model transient thermal impedance, package-to-case interfaces, heatsinks, board spreading resistance, load duty cycle, current limiting, thermal shutdown cycling, or regulator-specific safe-operating-area behavior.

Use defensible inputs

VIN: use the worst-case voltage at the regulator pin, not the supply label.
Dropout: prefer the maximum at relevant load and temperature over a headline typical.
θJA: match package, copper area, board stack, and airflow as closely as the manufacturer’s datasheet permits.
Junction limit: use the recommended operating boundary for the exact grade when it is lower than absolute maximum.

Stop conditions

Stop if electrical headroom is negative, the estimate reaches the entered junction limit, or the design depends on a best-case typical thermal number. A positive calculator margin is permission to verify, not proof that the assembly is safe.

Choose the exact regulator

Comparing 1117-family parts? Read the AMS1117, LM1117, and TLV1117 comparison before transferring one manufacturer’s limits to another part.

Change the architecture when needed

The PCB power-tree design guide and the voltage-regulator selection surface connect this estimate to switching conversion, rail sequencing, and verified parts.