Load calculator

The load calculator builds an NEC Article 220 load calculation for a dwelling or commercial building and turns it into a PDF you can hand to a customer or inspector. This page covers creating, editing and sharing a calculation.

Watch a demo

Where to start

• In your dashboard. Click Load calculations in the left menu. Calculations made here are saved to your account.
• The free calculator. Anyone can try the free load calculator without signing in. You need a free account (no credit card) to unlock the final calculation and get the PDF.

If you already have an account, use the dashboard. When you are signed in, the free calculator warns that its calculation will not be saved to your dashboard.

Create a load calculation

1. Go to Load calculations and click New.
2. Enter the property address.
3. Choose Dwelling or Commercial with the toggle next to the section title.
4. For a dwelling, pick a Calculation method: Standard - NEC 220 Part III or Optional - NEC 220 Part IV. NEC 2026 versions of both are listed and marked Beta. Then set the Nominal voltage, Number of dwellings and Dwelling condition.
5. For a commercial building, set the Property condition, Occupancy type, Nominal voltage and NEC version.
6. Work through each load section below. Click Add equipment to add a line.
7. Check the Final calculation at the bottom, then click Create load calculation.

For equipment that is not in the list, click Add equipment, then Add a line with your own values.

Edit a load calculation

1. Open the calculation from Load calculations.
2. Click Edit and make your changes.
3. Click Save and view. You can also press Ctrl+S (Cmd+S on a Mac) to save and keep editing.

Editing a saved calculation needs a paid plan.

Share, download or print

Open the calculation and use the buttons at the top: Share, Download or Print. Share gives you two options:

• Invite team member to edit adds that person to your account.
• Send PDF via email only emails a PDF copy. Type the address and click Share PDF. Nothing changes on your account or bill.

Free plan and Commercial features

• A free account can create 2 load calculations. After that, and to edit a saved calculation, you need a paid plan.
• Commercial calculations, commercial and 3-phase voltages, and buildings with more than 4 dwelling units need the Commercial Pro plan. See pricing.

Frequently asked questions

Is the load calculator NEC compliant?

It's built on the NEC standard and optional calculation methods: Article 220 for the 2017 to 2023 editions, and Article 120 for NEC 2026 (in Beta).

The math is fixed formulas written from the code, so the same inputs always give you the same result. Kopperfield AI can add lines for you, but it never does the math. We test the formulas against worked examples and real calculations every time we change them. If we find a mistake that changed your result, we fix it and let you know.

The calculator and the PDF show the NEC section behind each subtotal, so you or your inspector can follow the work.

A couple of things it doesn't do yet: the optional method on 3-phase services (use the standard method), and the existing-service calculation from measured maximum demand (220.87 / 120.87).

You still sign off on the result, so check your inputs and what your AHJ enforces. See our Terms of Service for the details.

Can I choose the NEC year?

Yes. On a commercial calculation, pick the edition in NEC version: 2017, 2020, 2023 or 2026 (Beta). On a dwelling calculation, choose in Calculation method between the Standard and Optional methods based on the 2017 to 2023 editions (Article 220) and the 2026 versions (Article 120, Beta).

How do I add a load shedding or load management line?

Right-click an equipment line (not inside a field). If that line supports it, choose Insert load balancing line.

Can I make load calculations on my phone?

Yes. In the mobile app, go to Tools, then Load calculation. See Mobile app.