Aisha K.
Mar 12, 2026
Clean layout and the results update instantly. Exactly what I needed for a quick planning check.
Electrical & Wiring
Electrical Subpanel Load Calculator
Required amps = sum of circuit loads × (1 + spare%).
Total load with spare percent → recommended subpanel size. Planning estimates only — verify measurements and local codes on site.
Inputs
10400
050
Smart analysis
Recommendations
Tailored to your live inputs and result—guidance only, not professional advice.
- Interpret
Treat this as a planning estimate
Primary result: Subpanel size = 80 A. Re-run with optimistic and pessimistic inputs to understand the range—not just a single point.
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Scenario A
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Plain-English guide
Terms & how it works
Confused by a field? Read the short definitions here while you use the tool.
Connected load (amps)
The “Connected load (amps)” value used in this tool’s formula. Adjust it to see results update live.
Spare capacity (%)
The “Spare capacity (%)” value used in this tool’s formula. Adjust it to see results update live.
How this calculator works
Total load with spare percent → recommended subpanel size. Planning estimates only — verify measurements and local codes on site. Required amps = sum of circuit loads × (1 + spare%). Example: 60 A connected load + 25% spare → 75 A subpanel minimum.
Required amps = sum of circuit loads × (1 + spare%).
Example: 60 A connected load + 25% spare → 75 A subpanel minimum.
When to use this Subpanel Load
Common use cases
- Total load with spare percent → recommended subpanel size.
- Sanity-check with this case: 60 A connected load + 25% spare → 75 A subpanel minimum.
- The relationship is: Required amps = sum of circuit loads × (1 + spare%).
Localized examples
- Electrical & Wiring: the example on this page uses the same formula as the widget.
What you get
- Fields: Connected load (amps), Spare capacity (%)
- Required amps = sum of circuit loads × (1 + spare%).
- Example on the page: 60 A connected load + 25% spare → 75 A subpanel minimum.
How to Calculate Subpanel Load Step-by-Step
- 1Enter Connected load (amps), Spare capacity (%). Use the values you have, not a catalog average, unless that is all you know.
- 2Required amps = sum of circuit loads × (1 + spare%).
- 3Worked case: 60 A connected load + 25% spare → 75 A subpanel minimum.
- 4Buy materials after you walk the job. This is a first-pass quantity, not a purchase order.
Governing formula
Required amps = sum of circuit loads × (1 + spare%).
60 A connected load + 25% spare → 75 A subpanel minimum.
Example: set Connected load (amps) = 60, Spare capacity (%) = 25, then read the result.
Variable definitions
- connectedLoadAmps
Connected load (amps)
The “Connected load (amps)” field. Default 60; typical range 10–400.
- sparePercent
Spare capacity (%)
The “Spare capacity (%)” field. Default 25; typical range 0–50.
- The takeoff (Required amps = sum of circuit loads × (1 + spare%).) ignores waste, code, and what you find when you open the wall. Measure twice on site.
- Nothing here is uploaded for the calculation itself.
Frequently Asked Questions
Required amps = sum of circuit loads × (1 + spare%).
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Community
Reviews & Ratings
See what others think about this tool, then leave your own rating to help improve CalculioHub.
4.8
out of 5.0
4 reviews
Daniel R.
Feb 28, 2026
Very usable on mobile. Would love a save/export option later, but the math feels solid.
Priya S.
Feb 3, 2026
The FAQ section answered my questions before I even had to search. Smooth dark mode too.
Marcus L.
Jan 19, 2026
Simple inputs, clear outputs. This replaced three bookmarks I used to juggle.
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