About AJ Designer

AJ Designer is a library of more than 270 free engineering and science calculators — physics, fluid mechanics, thermodynamics, engineering design, environmental and water systems, math, and finance. No signups, no paywalls, no data collection. Just the tools and context you need to get a reliable answer.

A brief history

AJ Designer started in the early 2000s as a small set of calculators I built for my own use — problems I was working through in school and wanted a faster way to check. I put them online because it was easier than keeping them on one machine, and over time other people started finding them.

What began as a handful of pages grew steadily into a library covering most of the calculation needs I encountered in my own engineering and software work. Much of the growth came from readers emailing to ask if I could add a particular formula or calculator — engineering students, practicing engineers, teachers, and hobbyists. Many of the calculators on this site exist because someone asked.

For most of that time the site ran on PHP. In 2026 I rebuilt it from the ground up on a modern static stack (Next.js) for better speed, accessibility, and maintainability. As part of the rebuild, every calculator page now includes a worked example, a primary reference, and a last-reviewed date.

How the calculators are built and verified

Every calculator is grounded in established engineering and physics references — Tipler's Physics for Scientists and Engineers, Lindeburg's Engineer in Training Reference Manual, and similar standard texts. Formulas are cross-checked against these sources, worked examples are computed and independently verified, and each page cites its primary reference.

Calculator logic, references, and examples are reviewed periodically, and each page shows when it was last reviewed. I also get bug reports and correction suggestions from readers — engineers, students, and teachers who spot an error, a typo, or a case where a formula's assumptions aren't clearly stated. Those reports have caught real mistakes over the years, and I treat reader feedback as one of the most valuable forms of review this site gets. I'd rather fix an error than defend one, so if you find one, please email me.

A note on appropriate use

These calculators are built for education, estimation, and first-pass engineering work. For safety-critical design decisions, use them as a starting point and validate against appropriate engineering standards and peer review.

About the author

Hi, I'm Jimmy Raymond. I started AJ Designer while working through problems in school at New Mexico Tech and the University of New Mexico, where I earned a B.S. in Environmental Engineering and a B.S. in Computer Science. The two degrees are what made this site possible — environmental engineering gave me the physics and dimensional-analysis foundation, and computer science gave me the tools to turn equations into software that someone else can pick up and use in thirty seconds.

In the years since, my professional work has taken me through safety-critical aerospace and space systems, real-time embedded software, and full-stack web development. I've shipped code to the standards used for aircraft, medical devices, and nuclear systems — contexts where “almost right” isn't right. That discipline is where the calculators on this site get their design philosophy: the formula has to be correct, the assumptions have to be stated, the units have to work out, and the limits of the tool have to be honest.

I've kept building this site for more than two decades because I enjoy the craft of it. There's a particular satisfaction in taking a messy real-world problem, finding the right equation, and turning it into something a stranger can use in thirty seconds to get a reliable answer. That's still why I do it.

I'm based in Albuquerque, New Mexico.

Contact

Email me at aj@ajdesigner.com for corrections, calculator requests, or general feedback. You can also find me on LinkedIn.

— Jimmy