Electrical Circuit Headroom Calculator — See What Capacity Remains
Find the planning margin left on an existing circuit and test a proposed addition without hiding the answer inside a total-load calculation.
Check your circuit
What circuit headroom means
Headroom is the difference between the planning ceiling you choose and the existing modeled current. The useful question is not only “how much is the circuit rated for?” but also “how much margin remains under the planning assumption I am using?”
Maximum additional load
This calculator also reverses the relationship. Once the existing current and planning ceiling are known, it can show the remaining current and its equivalent watts or VA under the same voltage assumptions.
Why the proposed addition matters
A circuit can have comfortable existing headroom but lose most of it when a heater, charger, compressor or other high-demand device is added. The before-and-after comparison makes that change explicit.
Example
At 230 V and 0.95 power factor, 1,800 W is approximately 8.24 A. An entered 16 A circuit with an 80% planning ceiling has a modeled ceiling of 12.8 A, leaving roughly 4.56 A before the proposed addition.
What is not included
This tool does not inspect conductor conditions, installation method, startup current, voltage drop, protective-device coordination, phase loading or local installation requirements.
Frequently asked questions
Does a positive result mean installation approval?
No. It only means the modeled load remains within your chosen mathematical planning ceiling.
Can I calculate the largest additional wattage?
Yes. The result includes maximum additional watts or VA supported by the modeled headroom.
Why is the power factor shown?
It allows a simplified conversion from watts to current while keeping the assumption visible.