Free Electrical Load Calculator for a Detached Garage Subpanel
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Are you planning to electrify your new or remodeled detached garage? The question, “How big of a subpanel do I need?” has to be at the top of your mind.
Optimize your detached garage subpanel effectively with my free online Electrical Load Calculator!
Determine the correct subpanel size by accurately calculating the combined load of all your garage equipment, from power tools to EV chargers. Ensure NEC code compliance and prevent circuit overloads for a safe and functional garage.
Detached Garage Electrical Load Calculator
Use this tool to estimate your total electrical load in VA (volt-amps). The calculator suggests an appropriate sub-panel size based on NEC guidelines.
How to Choose the Right Detached Garage Subpanel Size
Electrifying a detached garage opens up a world of possibilities — from EV charging to heavy-duty woodworking tools — but it also introduces a critical question: How big of a subpanel do I need?
This is where my free Electrical Load Calculator comes in. Whether you’re planning a workshop, studio, or charging station, the calculator helps you accurately size your subpanel based on your equipment and usage, ensuring code compliance and long-term safety.
What Is a Detached Garage Subpanel?
A subpanel is a smaller service panel that distributes electricity to a specific area — in this case, your detached garage. It connects to your main panel but acts as a local hub for breakers, making it easier to manage and expand circuits in the garage.
Unlike your main service panel, a subpanel doesn’t meter electricity; it simply redistributes it. If your garage is more than a few feet from your home or if you’re powering multiple 120V or 240V circuits, you need a subpanel.
For a deeper look into NEC subpanel rules, check out Detached Garage Electrical Code, especially the section on Sub-panels for Detached Garages, which explains why they’re essential for high-load equipment and multiple circuits.
Why Accurate Load Calculation Matters
Choosing the right subpanel isn’t about guesswork. It’s about matching your panel size to your actual power needs.
Install a panel that’s too small, and you risk tripped breakers, overheating wires, and possible code violations. Go too large, and you’re overpaying for materials — plus, the wiring and breaker sizes will also need to increase.
My calculator uses NEC guidelines to help you size it right the first time. It also helps ensure your setup remains compliant with code, which is crucial for insurance, resale, and permit approvals.
What to Include in Your Garage Load Calculation
To calculate your garage’s electrical load, think about what you’ll use now — and what you might add later.
Common garage equipment includes:
- General-purpose outlets and LED lighting
- Power tools: table saws, planers, welders, grinders
- HVAC units or mini-splits
- Fridges, freezers, air compressors
- EV chargers (Level 1 or Level 2)
- Home offices or hobby electronics
When estimating load, consider which items may run at the same time. For example, you probably won’t use a table saw and a welder simultaneously, but your EV charger might run while you’re using other tools.
How the Electrical Load Calculator Works
My Electrical Load Calculator estimates your total demand in VA (volt-amps) based on the inputs you provide. Once it tallies the total load, it recommends a subpanel size that can safely handle the demand, while leaving some margin for growth.
The calculator:
- Adds all itemized loads
- Suggests a minimum panel size in amps (30A, 60A, 100A, etc.)
- Helps you choose the right subpanel and plan your circuits accordingly
Not sure how to go from load calculation to installation? My guide, How to Install a Detached Garage Subpanel, walks you through the process — including how to pull cable from the main panel, choose conduit size, and wire breakers.
How to Interpret the Calculator Results
Let’s say your total calculated load is 9,600 VA. Divide that by 240V, and you get 40 amps. You could go with a 40A subpanel — but choosing a 60A panel gives you headroom for future tools or charging needs.
Use these rough VA-to-amp conversions:
- 30A panel → Up to ~7,200 VA
- 60A panel → Up to ~14,400 VA
- 100A panel → Up to ~24,000 VA
Also consider:
- Future expansion: Will you add more circuits later?
- Dedicated circuits: EV chargers and HVAC often need their own breakers.
- Distance from the main panel: Longer wire runs may require upsizing conductors.
What to Do After You Calculate the Load
Once you’ve used the calculator and determined your garage’s total load:
- Select a subpanel rated slightly above your total demand.
- Confirm wire size and conduit type, based on panel distance and amperage.
- Get a permit if required — your city or county may want to inspect the installation.
- Consult a licensed electrician, especially if you’re not experienced with residential wiring.
Conclusion: Start Your Garage Electrical Plan the Right Way
Sizing your detached garage subpanel correctly is one of the most important steps in any garage wiring project. It ensures your space is safe, up to code, and ready for whatever tools, appliances, or EV chargers you want to add.
Use the free Electrical Load Calculator above to get an estimate and choose a panel that fits your needs.
