Measure your barrel, click calculate, and get the exact mainspring height, thickness and length you need — no more ordering by guesswork.
⭐ At a glance
✅ Works for watches and clocks — manual wind, automatic, pocket watch and clock movements
📦 Included: USB stick with calculator software, PDF user guide and single-user commercial licence
✔️ Condition: New
✅ Runs in any browser — Windows, Mac, tablet or phone, no installation and no internet needed after first open
🔧 What it does & how to use
This is a single HTML calculator that turns your barrel measurements into a full mainspring specification — height, thickness (with a working range), length and material — so you can order the right spring first time. It's built for watch repairers who order mainsprings regularly, hobbyist watchmakers, clock repairers and horology students. A Verify mode lets you check whether a spring you already have will fit a given barrel, and an interactive diagram shows the spring sitting inside the barrel as you type, with a colour-coded fill indicator (green = ideal, amber = tight, red = overfilled). Six built-in presets are included for ETA 2824-2, ETA 2892-A2, Miyota 9015, Unitas 6497, Sellita SW200 and Seiko NH35.
- Measure the barrel: take the internal diameter, depth and arbor diameter
- Choose your type: select watch or clock and your desired power reserve
- Calculate: click Calculate to get the recommended mainspring specification instantly
- Check a spring you have: use Verify mode to confirm an existing spring fits the barrel
- Copy your result: use the clipboard copy or print-friendly output to paste straight into a supplier order
The calculator opens by double-clicking the HTML file — no install, works offline after the first open, and there's no subscription; you own it outright. It ships on a branded USB stick with the calculator, the full PDF user guide and your licence.
⚠️ Please check — results are estimates based on standard horological formulas; always cross-check against your supplier's specifications before placing an order.
