Estimate panel capacity from connected electrical loads accurately. Review demand current and future expansion needs. Plan smarter upgrades with clear electrical sizing guidance today.
| System | Voltage | Non Continuous Load | Continuous Load | Largest Motor | Demand Factor | Growth | Suggested Breaker | Suggested Spaces |
|---|---|---|---|---|---|---|---|---|
| Single Phase | 240 V | 18,000 W | 6,000 W | 3,000 W | 85% | 20% | 125 A | 24 |
| Three Phase | 415 V | 32,000 W | 8,000 W | 5,500 W | 80% | 25% | 80 A | 30 |
| Single Phase | 120 V | 9,500 W | 2,500 W | 1,200 W | 90% | 15% | 125 A | 20 |
Demanded Non Continuous Load = Non Continuous Load × Demand Factor
Continuous Design Load = Continuous Load × 1.25
Largest Motor Adder = Largest Motor Load × 0.25
Base Design Load = Demanded Non Continuous Load + Continuous Design Load + Largest Motor Adder
Final Design Load = Base Design Load × (1 + Future Growth Allowance)
Single Phase Current = Final Design Load ÷ (Voltage × Power Factor)
Three Phase Current = Final Design Load ÷ (√3 × Voltage × Power Factor)
Recommended Spaces = Existing Circuits × (1 + Spare Space Target)
The calculator rounds the current result up to a standard breaker size. It also rounds the space result up to a common panel space count.
Choose single phase or three phase power first.
Enter the operating voltage for the panel you are planning.
Add all non continuous connected watts.
Add all continuous watts that run for long periods.
Enter the largest motor load in watts.
Set a realistic demand factor for the installation.
Enter power factor, especially for motor or mixed loads.
Add future growth allowance to reserve upgrade capacity.
Enter your current number of branch circuits.
Set a spare space percentage for later additions.
Press the calculate button.
Review the estimated current, breaker size, and panel spaces shown below the header.
Use the CSV or PDF buttons to save the result.
A breaker panel size calculator helps you match electrical demand to a suitable service rating. That prevents overloaded equipment and supports safer expansion. Many homes add appliances over time. Load planning becomes more important with every new circuit. This calculator estimates design watts, operating current, and recommended panel size. It also checks future growth and panel space needs. That makes it useful for remodels, garage upgrades, office fit outs, and small commercial planning. Clear numbers help you compare options before buying equipment or requesting installation work.
Correct panel sizing starts with understanding the load mix. Non continuous loads run in normal cycles. Continuous loads operate for longer periods and often require extra capacity. Motor loads can raise starting demand. Demand factor reduces connected load to a more realistic design value. Future growth reserves room for circuits. Power factor affects current because lower efficiency increases amperage. Voltage and phase type also matter. A single phase service and a three phase service do not carry the same current for the same wattage. That is why accurate input choices improve sizing accuracy.
A well sized panel supports safety, maintenance, and expansion. If the main breaker is too small, nuisance trips become more likely. If the panel has too few spaces, future additions become harder and costlier. Good planning leaves room for HVAC upgrades, kitchen circuits, chargers, tools, and lighting changes. This calculator suggests a standard breaker size above the estimated current. It also recommends a practical panel space count. Those two outputs help you review both electrical capacity and physical circuit capacity. Always compare the estimate with local code rules and site conditions before final installation.
Use this tool during design, estimating, or project review. Enter non continuous load watts, continuous load watts, largest motor watts, voltage, demand factor, power factor, and growth allowance. Then add the number of circuits and spare space target. Submit the form to view the result under the header. You can export the result as CSV or PDF for records. The example table below shows a planning case. For final engineering approval, confirm conductor sizing, fault duty, grounding, service entrance conditions, and jurisdiction requirements with a qualified electrician.
It estimates design load, current, a recommended main breaker size, and a suggested panel space count. It is meant for planning and comparison before final code review.
Continuous loads often require extra design margin because they operate for long durations. Using 125% helps reflect common electrical planning practice for sustained demand.
Motors can add extra demand during operation and startup conditions. The motor adder helps create a more conservative estimate for service and panel planning.
Demand factor reduces connected non continuous load to a more realistic operating value. It helps avoid sizing the panel only from worst case connected watt totals.
Use the option that matches the actual electrical service. Homes often use single phase. Many commercial installations use three phase for improved load handling.
Spare spaces make future circuits easier to add. They reduce the chance of replacing the whole panel when new loads, appliances, or equipment are installed later.
No. It is a rounded planning result based on the entered values. Final selection must match local electrical code, equipment ratings, and site conditions.
Yes. It works well for early residential and small commercial load reviews. Final engineering checks are still necessary before purchase, permitting, or installation.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.