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Service Entrance Calculator

Estimate electrical service amperage from connected load, demand factor, and service voltage.

Updated April 18, 2026
Free online tool
Planning and research use

Why this page exists

Early electrical planning gets easier when connected load and demand assumptions are turned into an estimated service amperage instead of being discussed only in general terms. This calculator helps visitors estimate electrical service size from total connected load, demand factor, and service voltage so they can see the rough service level their assumptions point toward.

Interactive tool

Run the estimate

Enter your numbers and read the result first, then use the sections below to understand what affects the outcome.

Calculator

Service entrance calculator

Estimate electrical service amperage from connected load, demand factor, and service voltage.

Result

120.00 A

Estimated service amperage from demand-adjusted load divided by the service voltage entered.

Estimated service amperage120.00 A

Demand-adjusted load28,800 W

Service voltage used240 V

Nearest common service size125 A

36,000 watts at a 80.0% demand factor reduces to about 28,800 watts of planning load.
At 240 volts, that planning load points to about 120.00 amps, which is closest to a common 125-amp service size.
Use the result as a first-pass planning number only, because code-based service calculations can be more detailed than a simple load-and-demand approach.

This is a simplified service-sizing estimate only. Real electrical service sizing depends on code rules, demand calculations, continuous loads, equipment specifics, and local inspection requirements.

Planning note

Last updated April 18, 2026. Use this tool to compare scenarios and plan ahead, then confirm important details with the lender, employer, insurer, contractor, or other qualified provider involved in the final decision.

How it works

What the calculator is doing

Enter total connected load, demand factor, and the service voltage you want to use.

The calculator reduces the connected load by the demand factor entered.

It divides the demand-adjusted load by service voltage to estimate amperage and shows the nearest common service size.

Understanding your result

This is a simplified planning estimate only. Real service sizing depends on code calculations, continuous-load rules, equipment mix, and local inspection requirements, so the result should not replace professional design or permitting decisions.

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Examples

Ways people use this tool

Example scenarios help turn a quick estimate into a more useful comparison or planning step.

Check whether a remodel may push service size higher

A first-pass amperage estimate can help show whether new appliances or added loads might justify a closer service review.

Compare load scenarios at different demand assumptions

Running a more conservative and less conservative demand factor can show how sensitive the estimated service size is to usage assumptions.

When to use it

Good times to run this calculator

Use this when you want a quick service-size estimate from a rough connected-load assumption.

It is especially useful during early remodel, equipment-upgrade, or property-planning conversations before a detailed electrical design is complete.

Assumptions and limitations

The estimate assumes the connected load and demand factor entered are reasonable for the property and use pattern.

It does not perform a full code load calculation, and it does not account for every rule tied to continuous loads, diversity, or equipment-specific sizing.

Common mistakes

Avoid the usual input mistakes

Treating total connected load like actual demand can overstate service needs if the demand factor is not considered carefully.

Using the nearest common service size as a final answer can be misleading because the real service decision may need a more formal calculation.

Practical tips

If the estimate lands near a service-size threshold, test a few demand assumptions before deciding whether an upgrade seems likely.

Review the result with appliance-energy and service-load tools so connected load, energy use, and service sizing stay aligned.

Worked example

Walk through a realistic scenario

A worked example shows how the estimate behaves when the inputs resemble a real planning decision.

Estimate service amperage from a remodel load

A homeowner wants to see whether an equipment upgrade may point toward a larger service before calling for quotes.

1. Enter the connected load, demand factor, and service voltage.

2. Review the demand-adjusted load and calculated amperage.

3. Compare the result with the nearest common service size as a first-pass planning check.

Takeaway: The tool is most helpful as an early sizing signal, not as a substitute for a code-based electrical calculation.

FAQ

Common questions

How is service amperage estimated here?

The calculator applies the demand factor to the connected load, then divides the adjusted load by the service voltage to estimate amperage.

Why does it show a nearest common service size too?

Because the raw amperage estimate is often easier to interpret when it is compared with common residential or light-commercial service sizes.

Can I use this instead of an electrician or code calculation?

No. This is a first-pass planning estimate only, and final service sizing should follow code rules and professional review where required.

Related tools

Keep comparing

Service-load, electricity-cost, Ohm's Law, and watt-hours tools help connect the amperage estimate to broader electrical planning and usage questions.

Appliance-energy and battery-charge tools add context when the next question is where the electrical demand is coming from and how it is used over time.

Home ToolsUpdated April 11, 2026