I Built a Free Workshop Calculator App — Here's How It Actually Happened
I didn't set out to build a web app.
I was trying to figure out how to space flat bars evenly across a welding table frame. Simple enough problem — take your total frame width, subtract the bar widths, divide the remaining space by the number of gaps. Except every time I tried to do it in my head or on a calculator, I'd lose track of what I was doing, second-guess myself, and end up measuring twice anyway.
I Googled it. Nothing useful came up. There were forum posts with someone's handwritten formula in the comments, a few Excel spreadsheets from 2009, and a lot of people saying "just measure it out on the floor." Not exactly what I was looking for.
So I built the thing myself.
What GapCalc Actually Is
GapCalc is a free, browser-based workshop calculator built for welders, fabricators, and makers. No login. No app to download. No paywalls. You open it on your phone in the workshop, and it works.
It started as one calculator — the Gap Calculator — which does exactly what I needed. You enter your frame dimension, your bar width, and your target gap, and it tells you how many bars fit and what the actual gap will be. Simple. Useful. Done.
That was version 1.0.
Since then, it's grown into something I didn't fully anticipate. GapCalc now has 15 tools covering most of what you'd need to plan and price a fabrication job:
- Gap Calculator — bar and slat spacing
- Cut List Calculator — cuts per length, offcut sizes, waste percentage
- Weight Calculator — steel and timber order weight with vehicle load indicator
- Angle Cuts — short point, long point, cut face length with a visual diagram
- Welding Rod Estimator — rod recommendation and quantity estimate by material, joint, and position
- MIG Wire Estimator — wire needed in kg and reels to buy
- MIG & Flux Core Settings Guide — starting point settings with machine capability toggles
- Weld Troubleshooter — plain English symptom descriptions, causes, and fixes for common weld problems
- Job Costing Calculator — material, labour, consumables, delivery, margin, and a professional client quote
- Bolt Spacing Calculator — fixing spacing with centre-to-centre and edge-to-edge modes
- Drill Bit & Tap Reference — tap drill, clearance, and countersink sizes for metric and imperial threads
- Job Timer — named task tracking that feeds directly into the Job Costing calculator
- Paint & Primer Coverage — litres or spray cans needed for any surface
- Sheet Metal Flat Pattern — flat blank size before bending
- Pipe & Tube Bending — developed length and tube marking instructions
All of it runs in a single HTML file. No framework, no database, no backend. Just vanilla HTML, CSS, and JavaScript hosted on Cloudflare Pages, connected to a GitHub repo, and deployed automatically every time I push an update.
How It Was Actually Built
Here's the honest version.
I'm not a developer. I've never studied computer science or worked as a software engineer. My background is in digital marketing and data — I work as a Data Automation Specialist at a marketing agency, so I understand systems and logic, but writing code from scratch isn't something I'd call a skill of mine.
What I can do is plan clearly, think through problems methodically, and use the tools available to me.
I started planning GapCalc in Gemini. I was using it to think through the logic, sketch out features, ask questions. It was useful to a point, but I kept hitting walls — the responses felt generic, and I struggled to get it to hold context across a longer planning session. It wasn't giving me what I needed.
Then I switched to Claude.
The difference was significant enough that I kept going. Claude helped me think through the formulas, plan the user interface, write the JavaScript, debug issues, and iterate on features — session after session, with enough context retention that it felt like working with someone who actually understood the project. I'm not going to pretend I wrote all the code myself, because I didn't. But I planned every feature, made every design decision, tested everything, and pushed every update. The workflow was: plan it here, confirm it makes sense, write a tight prompt, implement in VS Code with Claude Code, review the diff, push to GitHub.
It works. And the app works. That's what matters to me.
The Technical Stack — For Anyone Curious
- Single HTML file — everything lives in one index.html. No build tools, no bundlers, no dependencies
- Vanilla JavaScript — no React, no Vue, no frameworks
- Google Fonts — Bebas Neue, DM Mono, DM Sans
- Cloudflare Pages — free hosting with global CDN and unlimited bandwidth
- GitHub — version control and auto-deploy trigger
- Google Analytics — basic traffic tracking
- Google Search Console — SEO monitoring
- VS Code + Claude Code — development environment
The no-framework decision was deliberate. GapCalc needs to work on a phone with a weak signal in a workshop. A single HTML file loads fast, works offline once cached, and has zero dependencies that can break. It also means anyone can open the source and understand what's happening — there's no magic.
What Surprised Me
The analytics surprised me first. Within the first month, GapCalc had visitors from 11 countries — United States, Ireland, Singapore, Netherlands, UK, Poland, South Korea, Sweden, and others. I built it for South African welders and fabricators. Turns out the problems it solves aren't unique to South Africa.
That changed how I think about the project. The Job Costing calculator now supports seven currencies. The language throughout the app has been updated to be internationally accessible. The drill reference includes imperial UNC threads alongside metric. The weight calculator includes Aluminium, Copper, and Brass alongside mild steel.
The second thing that surprised me was how many small decisions compound into something that feels complete. Every feature was designed around one question: what does someone actually need to know before they make a cut, strike an arc, or send a quote? Not what's technically impressive — what's actually useful at 7am in a cold workshop with dirty hands and a phone screen you can barely read in the sun.
What's Next
GapCalc is free and always will be. That's not a marketing line — it's a decision I made early, and I'm sticking to it. The tools you need to plan your work shouldn't cost money.
That said, the project does need to sustain itself at some point. The roadmap includes some paid features down the line — PDF quote export from the Job Costing calculator is the most likely first candidate — but the core tools will stay free regardless.
I'm also working on a second project called Zink. — a similar concept but built for writers, publishers, SEO professionals, and marketers. Same philosophy: free, no login, no paywalls. Still in development, but worth keeping an eye on.
In the meantime, the best thing you can do if you find GapCalc useful is share it. Tell someone in your workshop, post it in a group, mention it in a comment. That's how a free tool with no advertising budget grows.
Watch It in Action
I'm putting together a short overview video showing how GapCalc works and walking through some of the key features. It'll be on my YouTube channel — subscribe at youtube.com/@heavymetalbren so you don't miss it when it drops.
If you've got questions, feature ideas, or just want to talk shop, come join The Forge Builds — a Facebook community for makers, welders, and DIY builders that I'm growing alongside the app. Or drop a comment on YouTube. Either way, I read everything.
Free. No login. No data collected. Works on your phone.
Brendan Glover brendanglover.github.io — linktr.ee/gloverbrendan
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