Overview
Type in the job, get the service size. Floor area, appliances, range, dryer, heat, air conditioning, EV charger. The workbook applies the demand factors, runs the tables, and returns the calculated load in amperes and the next standard service size per 240.6(A). Then you print one page and hand it to the inspector.
It runs both code editions. You pick 2023 or 2026 on the Settings tab and the whole workbook follows: section numbers, unit loads, demand factors, tier thresholds, EVSE rules. One cell. If you want to see where a section moved before you buy anything, the free NEC 2026 code translator is on this site and does that part for nothing.
The change that broke every older worksheet
The 2026 NEC moved load calculations out of Article 220 and into Article 120, and cut the dwelling unit load from 3 VA per square foot to 2. Any load calc sheet written before that change returns the wrong number on a 2026 job, and it returns it confidently, which is worse.
Most of the renumbering follows a clean pattern, but not all of it, and the parts that do not follow the pattern are the parts that change your answer.
The trap it catches
Under the 2026 NEC a dwelling uses two different unit loads, and they are not interchangeable. 120.41 sets 2 VA per square foot for feeder and service sizing. 120.13 keeps 3 VA per square foot for the minimum branch circuit count.
Use 2 for both and you short the circuit count. Use 3 for both and you oversize the service and lose the bid. This workbook calculates them separately so they cannot get crossed.
The retrofit calculation
Section 120.83 is where the 2026 code does the most for a contractor, and it is the tab that pays for the workbook.
Take a 2,000 square foot house on a 100 amp service, adding a 7.2 kW EV charger. Under the 2023 NEC it calculates at 108.7 amps, it fails, and you are quoting a service upgrade. Under the 2026 NEC the new-load demand factors bring it to 99.3 amps and it passes.
Same house, same charger, different answer. The Existing Dwelling tab runs both editions and tells you pass or fail against the service that is already in the house, which is the question the customer is actually asking.
What's inside
An Excel workbook with nine working tabs:
- Settings. The edition switch and every constant the calculations use.
- Standard Method. The full itemized calculation, plus the minimum branch circuit count.
- Optional Method. 120.82 and 220.82. Runs all six heating and cooling scenarios and takes the largest, because that is what the code requires.
- Existing Dwelling. Adding load to a service that is already there. Pass or fail, and what the service would need to be.
- Multifamily. Two or more units on one service.
- Permit Sheet. One page, print ready, code basis printed on it, signature block.
- 2023 vs 2026. Every section that moved, and what actually changed.
- NEC Tables. Left visible so you can check the math yourself.
Plus two PDFs: a 5 page landscape Field Reference with the full 2023 to 2026 mapping, both methods side by side and a worked example, and a 3 page Quick Start Guide.
Why the numbers hold up
- Every calculated line cites its NEC section, in both editions. If an inspector questions a number, you point at the row.
- Range demand handles Column A, Column B and Column C properly, including the Note 1 uplift above 12 kW.
- Dryer factors run past the printed table instead of returning garbage at high unit counts.
- The service size ladder carries every standard rating in 240.6(A) from 15 amps to 6000, so a 105 amp load returns 110 and not 125.
- Formula cells are protected so you cannot wreck it by accident. There is no password, so unprotect the sheet and extend it if you want to.
Who it's for
Electricians sizing services and feeders. Contractors quoting panel upgrades, EV chargers and heat pump retrofits. Anyone who has to put a load calculation in front of an inspector and wants the numbers to hold up when they are questioned.
What this is not
This part is here so nobody buys the wrong tool.
- It is not a panel schedule. This sizes a service or feeder from a load calculation. If you want to lay out circuits, balance the legs and print a directory for the panel door, that is a different tool.
- It covers dwelling units. Single family under the standard and optional methods, existing dwellings adding load, and multifamily. Not commercial occupancy calculations, farm loads or health care facilities.
- It does not do voltage drop, conduit fill, short circuit current or arc flash.
- Two values depend on a reading of the code text I could not confirm from a published source, and I would rather say so than pretend otherwise. The optional method lighting density is set to 3 VA per square foot, the conservative reading, because the 2026 cut to 2 VA is documented for feeder and service sizing under 120.41 and not for the optional method. And 120.57 is implemented as nameplate where known. Both are one cell on the Settings tab if your codebook reads differently, and there is a note on the tab where each one lives.
- Publication and adoption are different dates. Plenty of jurisdictions are still enforcing an older edition and local amendments override the national text. Confirm what your AHJ has adopted and set the workbook to match.
- The signature is yours. This workbook applies the calculation rules. It does not know your jobsite. The licensed person signing the permit owns the result.
Compatibility
Microsoft Excel, Google Sheets and LibreOffice. No array formulas, no newer Excel-only functions, nothing that breaks on import. Windows, Mac, iPad and Android. No subscription, no login, no expiry.
Works best with
Tradesman Office products are designed to work together, so what you buy here compounds instead of sitting alone in a folder.
- Electrician Flat Rate Price Book, for pricing the service upgrade once the calculation says you need one
- NEC Code Quick Reference Guide, for the sections this workbook cites
See the full system on our How It All Works page.
Why buy from Tradesman Office
Every product in the shop was built by a tradesman who did this work in the field, which is why they are calibrated to the problems that show up on a job rather than the problems a software designer guessed at.
- Excel-first. Buy once, own forever. No subscription, no vendor lock-in.
- Works on any device. Excel, Google Sheets, iPad, wherever you quote from.
- Part of a complete system. Every product here works with the others. See the full flow on our How It All Works page.
- Fast support. Message through Etsy and get a response from the founder within one business day.