7 Brew Caffeine Calculator

There's a 7 Brew two minutes from my house. I've been going almost daily.

At some point I started wondering how much caffeine am I actually putting in my body? Not a rough guess. The real number, accounting for size and the extra espresso shots I keep adding.

There was no tool for this. The 7 Brew app doesn't show caffeine. Google gives you ballpark estimates at best. So I built what I wanted to exist.

It started as a spreadsheet.

Literally a Google Sheet where I manually entered caffeine values per drink per size and dragged a formula down. It worked. It was also embarrassing to open in public.

So I wrapped it in a browser extension instead.

What it does:

Click the toolbar icon → pick a drink → choose size → add extra shots → done. You get caffeine in mg, calories, an energy level (Low / Moderate / High / Extreme), and a circular gauge showing where you are against the FDA's 400mg daily limit. It also lets you save favorite orders and reload them as one-tap pills.

I shipped a matching browser theme alongside it deep espresso charcoal + neon blue because if I'm going to open something ten times a week it might as well feel intentional.

What I actually spent time on:

Not the math. The math is trivial.

The real work was:

1. Building one source, three browsers. Chrome, Edge, and Firefox all speak Manifest V3 now but with enough differences to be annoying. Firefox needs a browser_specific_settings.gecko block. The data_collection_permissions field is Firefox-only and will get your AMO submission flagged if it's missing. I wrote a small Python sync script so I only ever edit one set of source files and it propagates to all three browser builds automatically.

2. Making the UI feel worth opening. I went further than I planned on the design, animated SVG progress ring, glassmorphic cards, neon glow states tied to energy levels, and micro-transitions on every interaction. Probably 60% of the total build time. Zero regrets.

3. Storage that doesn't require an account. Everything lives in chrome.storage.local. No backend, no auth, no email, no analytics. Favorites persist across sessions without any of that friction. I almost added a sync feature and talked myself out of it.

Numbers that surprised me:

• Under 50KB total, unzipped, across all three browsers

• The only permission requested is storage solely for saving favorites

• Cold Brew + Large + 2 extra shots = 550mg caffeine. I don't recommend it. I've done it.

What I'd do differently:

Start with Firefox. Chrome is the obvious default, but Firefox's stricter manifest requirements catch you at the end if you build Chrome-first. Start Firefox-first and Chrome just works.

What's next:

A daily intake tracker with a midnight reset, and a half-life calculator so you know when the caffeine actually clears your system. Might be overkill for a coffee chain extension. Building it anyway.