SolarCalcWorks is a set of free calculators for sizing solar power systems. Every one of them shows the code section, the table and the arithmetic behind its result, so you can check the work instead of trusting a number.
Why it exists
Search for a solar wire size calculator and you will find dozens of them. Most return a single number with no indication of where it came from. Several disagree with each other on identical inputs, usually because they run one of the two required checks and ignore the other, or because they apply the NEC's 125 % rules in a way the code does not actually require.
That is a bad situation for someone standing in a hardware aisle deciding between 6 AWG and 4 AWG. The difference is real money, and in the other direction it is a fire risk. What that person needs is not a faster number — it is a number they can verify.
So the design goal here is unusual for a free tool: every result is auditable. The calculator names the table it read, the correction factors it applied, the threshold each test had to clear, and which of the two requirements produced your final size. If you have a code book on the bench, you can follow along line by line.
Editorial standards
- No invented figures. Statistics, ampacities and resistance values are either taken from a named published source or computed from first principles. If we cannot source a number, we do not publish it.
- Mandatory and advisory are never conflated. Ampacity is a code requirement. Voltage drop is a design recommendation carried in an informational note. The tools label which is which every time.
- Limitations are stated up front. The methodology page lists what the calculators deliberately do not model, because knowing when a tool does not apply matters more than knowing when it does.
- Pages exist because they are useful. We publish a page for a specific use case when that use case genuinely changes the advice — not to occupy a search term. Tools still in development are listed as such rather than given empty placeholder pages.
What this is not
These are design aids. They are not a substitute for a licensed electrician, an engineered design, or the judgement of your local authority having jurisdiction. Codes vary by jurisdiction and by adopted edition, and a permitted installation needs someone qualified to sign off on it. Use these tools to understand your system and to check someone else's numbers — not as the final authority on an installation.
How it is funded
The calculators are free and always will be. There is no account, no paywall, no gated result and no email capture. The site is intended to be supported by advertising, and possibly by affiliate links to relevant components in future.
Two commitments about that. Advertising will never sit between an input and its result, and no calculation will ever be influenced by what a product recommendation pays. If affiliate links appear, they will be disclosed where they appear, not buried in a footer. A sizing tool that steers its answers toward a payout is worthless, and we would rather have a smaller site that people trust.
Corrections
If you find an error in a calculation, a table or an explanation, we want to hear about it. A mistake in a tool like this can end up inside somebody's wall. Get in touch with the inputs you used and the result you expected.