Role
Design, mobile, backend, web
All case studies
Trade Calculator App · Live
CalcRig
A field calculator for the trades — 16+ code-cited calculators across electrical, HVAC, plumbing, and construction, built to work offline on a job site.
iOSAndroidiPad
Platforms
iOS · Android · iPad
Type
Cross-platform app + API
Status
Live · 2026
Overview
CalcRig is a multi-trade field calculator for construction, HVAC, electrical, and plumbing professionals. Instead of juggling a handful of single-purpose apps and a code book, a tradesperson gets 16+ calculators in one place — each one showing the formula it used and the code section it's based on.
We built it offline-first because job sites rarely have reliable signal, and we made every result something you can hand to an inspector: the wire-ampacity number sits next to its NEC table reference, the duct-sizing result next to its ASHRAE basis.
The problem
What we set out to solve
Trade calculation tools are fragmented — one app for wire sizing, another for duct sizing, and a code book to verify either. Switching between them mid-task is slow and error-prone.
The free alternatives are shallow: they spit out a number with no formula and no code reference, so the result is impossible to defend to an inspector or a client.
And almost none of them work where the work happens. Job sites have patchy connectivity, so anything that depends on a live network is unusable exactly when it's needed.
Our approach
How we built it
We treated CalcRig as a precision instrument first and an app second. The calculation logic had to be trustworthy, transparent, and available with zero connectivity — everything else was built around that.
01
Pure, testable calculation engine
Every calculator is a pure TypeScript function separated from the UI, returning both the value and the formula used. That keeps 16+ calculators consistent and verifiable, and lets us cite the exact code standard behind each result.
02
Offline-first data layer
Calculations and projects are stored locally in SQLite (op-sqlite + Drizzle) so the app is fully usable with no signal. A sync queue reconciles changes with the backend when a connection returns.
03
Trade-organised navigation
Each trade gets its own tab and stack, so an electrician lands on electrical tools and a plumber on plumbing — no hunting through a flat list of dozens of calculators.
04
One brand across app, web, and store
A locked design system (construction-orange accent, four trade colours, iOS-native typography) keeps the marketing site, app, and store assets feeling like one product.
Capabilities
What it does
Code-referenced results
Every calculation shows the formula used and the standard behind it — NEC, ASHRAE, UPC, or IRC. Results you can cite to an inspector.
Pure calculation engine
All calculation logic lives in pure TypeScript functions, separate from the UI — testable, reliable, and consistent across all 16+ calculators.
Offline-first
Local SQLite storage means the app works with zero connectivity. A sync queue pushes changes to the cloud once you're back online.
Calculation history
Full parameter persistence — restore any past calculation, tweak the inputs, and recalculate. Organised by project, not just a log of numbers.
PDF & share export
Turn any result into a branded PDF or share it as formatted text — for quotes, estimates, or client handoff.
Built for the field
High-contrast dark UI, large tap targets, imperial/metric toggle on every calculator — designed for sunlight, gloves, and real conditions.
Under the hood
Architecture
CalcRig spans three surfaces — a cross-platform app, a type-safe API, and a marketing site — that share a single design language and a generated, end-to-end-typed contract between client and server.
Mobile app
Expo Router app with per-trade tab navigation. Local-first state in SQLite via Drizzle, fast preferences in MMKV, server state through React Query. Auth, entitlements, and sync are layered as providers at the root.
React Native 0.83Expo 55NativeWind v5op-sqlite + DrizzleJotaiReact Query
Backend API
A Hono + PostgreSQL service publishing an OpenAPI spec. Sync endpoints reconcile the device's offline queue with server state using version numbers and server-wins conflict resolution.
HonoDrizzle ORMPostgreSQLBetter-AuthOpenAPI / Scalar
Type-safe client
The app's API client and React Query hooks are generated from the backend's OpenAPI spec with Orval, so a schema change on the server surfaces as a type error in the app — no hand-written, drift-prone models.
OrvalAxiosZod
Tech stack
Built with
Mobile app
React Native 0.83
Cross-platform native app
Expo SDK 55
Managed native workflow + EAS
Expo Router
Per-trade tab navigation
NativeWind v5
Tailwind v4 in React Native
Data & state
op-sqlite
Local SQLite database
Drizzle ORM
Type-safe history schema
MMKV
Fast preferences storage
React Query
Server state + sync
Backend & platform
Hono + Postgres
Type-safe REST API
Better-Auth
Email, Apple & anonymous auth
Orval
Generated React Query client
RevenueCat
Subscriptions & paywall
Hard parts
Engineering challenges
Challenge
Stay fully usable with no signal, then sync without losing or clobbering data when connectivity returns.
Solution
An on-device sync queue records every offline change. On reconnect, the app pushes the queue and pulls deltas keyed by a server-assigned version number, with server-wins resolution and exponential backoff — so the app degrades gracefully and never blocks the user offline.
Challenge
Keep 16+ calculators and a separate backend in lockstep without hand-maintaining API models.
Solution
The backend emits an OpenAPI spec; Orval generates the app's typed client and React Query hooks from it. A breaking server change becomes a compile-time error in the app instead of a runtime surprise.
Challenge
Gate Pro features by subscription while keeping a single source of truth for who the user is.
Solution
RevenueCat entitlements are linked to the Better-Auth user ID on login, so paywall state and account state never diverge — cloud sync, unlimited history, and PDF export unlock cleanly against one identity.
Screens
A look inside
Outcome
What shipped
Shipped to iOS, Android, and iPad from a single React Native codebase.
Every calculation is fully usable offline and carries its formula and code citation.
16+ calculators across four trades, unified under one navigation model and design system.
A generated, end-to-end-typed contract between app and backend that prevents API drift.
Free tier plus a Pro subscription (cloud sync, unlimited history, PDF export) handled through RevenueCat.
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