A Czech carpenter's €12.99 calculator ranks #1 on paid utility charts in three countries

A registered carpenter in the Czech Republic turned what he calculates in his workshop every day into an app: how to lay out drawers, how to cut the panels, where to drill, and a PDF to take to the shop once it's done. One-time purchase of €12.99, no subscription. Six weeks after the iOS launch, it has hit #1 on the paid utility charts in the Czech Republic, Slovakia and Hungary; after a 30% price increase it climbed back to #1. It's not a big business, but it shows how a small tool should be built: people who know the trade turn manufacturer manuals into calculators.

A post saying "thanks for waiting for the iOS version"

On 2026 Sep 16, the Instagram account @truhlarskakalkulacka posted: "The carpenter's calculator now also has iPhone and iPad versions. Thanks to everyone who wrote in and has been waiting for the iOS version." The top comment came from a woodworking shop account: "Really great helper!!!" The second was in Slovak: "Great, can't wait to try it."

The post got only 8 likes. The author is Petr Hanč; Czech business registration lists his main activity as woodworking, and his trading name is HANČ NÁBYTEK, a furniture maker. There's only this one app under his developer account. The Android version went live on Google Play in Aug 8, and by Nov 6 had 788 installs, each worth $12.99 (Google Play install count, 11-06). When iOS launched, the people who had written in waiting were ready-made first buyers.

A month later, a user in Germany left the only written review so far, titled "A good app that keeps growing": "It already covers a lot of the hardware I use. Calculating drawers—I'm using Blum's Legrabox here—is very simple and clear. Choosing spring force for lift-up fittings is also calculated precisely." (App Store Germany, 10-15,5 stars)

What it calculates

A cabinetmaker, for every finished drawer system installed (Blum's Legrabox and Tandembox, Hettich's ArciTech and similar), has to look through hardware manufacturers' technical manuals: from the cabinet's internal width, depth and drawer height, work out the side, back and bottom panel sizes by hand, then calculate the drilling positions for the runners on the cabinet sides and the drilling positions on the back of the door panels. One wrong number and a board is ruined.

The app turns "look up the manual + calculate by hand" into "enter the cabinet dimensions, get the result":

• How several drawers fit in one cabinet, the height of panels and drawers, and where they'll clash; it warns you;
• The cut size of each panel in every drawer, which can be copied directly;
• A drilling diagram for the cabinet sides and the back of each door panel, with dimensions marked;
• Blum's six types of lift-up hardware (AVENTOS), with spring selection based on panel weight;
• Shelves, hinges, handle holes, cutlery trays, and even "how many meters of edge banding are left on this roll";
• Finally, a PDF with dimensioned drawings, which you can save, send to the installer, or print to take to the workshop.

Covers eight brands: Blum, Hettich, Häfele, GRASS, GTV, Strong, Level and AMIX, with 18 finished drawer systems alone (official site and App Store description, 11-06). Works offline, no registration, no ads. The interface is available in six languages: Czech, Slovak, Polish, German, Hungarian and English; the October 1.0.9 update also added Blum's US models, with inch and 1/32-inch fractional input.

Only the people who work in the workshop every day know what should be built and how to build it right. Factories have their own tools too, but Blum's cabinet configurator is a web page that requires signup and leans toward product selection and ordering, while EASY ASSEMBLY is an installation tutorial video. They all only cover their own brands, and none of them will directly output a cut list and drill pattern for your specific cabinet dimensions.

How it's actually selling

(App Store charts by country, 10-28 to 11-06)

Global ratings went from 19 in late Oct 28 to 27 in Nov 6, 8 in ten days. The number is small, but for a €12.99 professional tool it shows real carpenters are buying every day.

There's a detail in the Hungarian row: Hungarian wasn't added until the 1.0.9 update at the end of October, and a few days later (11-03) the Hungarian store jumped straight to #1 in Top Paid Utilities (inferred: adding one language opened up one country).

In Nov 2, it raised the price from €9.99 to €12.99, the Czech store from 239 to 299 CZK, and Poland from 39.99 to 54.99 złoty. After the increase, the Czech store 11-04 and 11-05 returned to #1 in Top Paid Utilities. Buyers aren't very price-sensitive. For someone who makes a living with their hands, €13 is less than the cost of one board.

The scale of the money needs to be clear: it's not big. On the Top Paid overall charts in the Czech Republic, Slovakia and Hungary, you only need single digits to a dozen-plus sales a day to make the top 20, so "#1" roughly means a few to a dozen-plus sales a day. iOS plus Android comes to an estimated monthly revenue of a few thousand euros (estimate, before Apple and Google's cuts and taxes). Android's 788 installs, roughly estimated, add up to lifetime revenue of €7,000–8,000 (estimate). Small but real, not a hit.

Where users come from

No media coverage, no discussion on X, and no TikTok creators or free-promo chart pushes found. Only four channels can be confirmed, all very plain:

The name is the search term. Its name in each country's store is the local-language "carpenter's calculator": Truhlářská kalkulačka in Czech, Schreiner-Rechner in German, Kalkulator stolarza in Polish, Stolárska kalkulačka in Slovak, Asztalos kalkulátor in Hungarian. When a carpenter searches for this term in the store, it's the first result. In small languages, almost nobody has claimed this term.

One homepage per language. Czech, German, Polish and English each have their own Facebook / Instagram page, posting illustrated tutorials and update notes. All are very small: the Polish page has 315 followers, the German page 25. The link on the Polish page carries a tracking parameter "launch_pl", and the privacy notice on the official site says they use their own analytics to "compare the effectiveness of promotions". The author opens country by country and keeps records. No evidence was found of paid Meta ads (unverified).

Early Android users. The Android version ran for over five weeks, building up several hundred paying users and a group of people waiting for iOS. When iOS launched, people bought it and left ratings.

Three updates a month, each one announced. Over 1.0.8 to 1.0.10, more than a month, there were three versions, each adding several hardware systems and one or two new calculators, with a long post in each language's homepage. The German post ends with: "Thanks everyone for the ideas and experience you bring from the workshop." The German review headline "Still expanding" refers to exactly this.

Plus one more point (inferred): the author is a registered carpenter, so the tool is naturally credible when shared within woodworking circles.

Who it's competing with

"Calculate drawers and drill positions by specific hardware model, export a workshop PDF offline on your phone, in multiple small languages": there is no established competitor in this spot yet. In Hungary, "Asztalos kalkulátor: Cutlist" was newly released in October; it calculates wood volume and cuts, which is not the same thing, so it doesn't count as a copycat.

If it were you

Verdict: Building an identical one has little point. It already holds the search terms in Central and Eastern Europe, and its author is a carpenter who adds hardware systems three times a month. You can't keep up with his industry knowledge. What's worth copying is the approach: find a trade where people constantly check manufacturer manuals and have to redo work when they get it wrong, build a calculator that outputs results by model, sell it as a one-time purchase, and open one language at a time.

Who it suits: Developers who have worked in, or have people around them working in, a hands-on trade (plumbing, electrical panel wiring, door and window hardware, stairs, tiling, air-conditioning installation), and people living in a European country with a small language who can talk to local tradespeople in their mother tongue.

Who it doesn't suit: Anyone with no industry knowledge who just wants to wrap a generic calculator shell. The value of this kind of app lies entirely in whether the model-level data and algorithms are right, and one wrong result will get buried in bad reviews. Anyone who wants subscription revenue or fast growth: the market is "a trade × a small country", and the ceiling is there.

How to build it: Start with a hardware or equipment category dominated by a few brands. Enter the manufacturers' public technical manuals model by model, and have a few real tradespeople verify the algorithms before release. The output must be something you can take to the site: clearly dimensioned diagrams and a printable PDF. Offline, no signup, no ads, one-time purchase, priced in the €10–15 range, and be willing to raise prices after launch. Validate on Android first, then go to iOS.

How to get users: Use the local-language trade term directly in the store name ("electrician calculator", "plumbing calculator"). It's the cheapest traffic there is. Open a separate Facebook / Instagram page for each language, posting illustrated tutorials and update posts, with tracking parameters in the links, and see which country picks up. Adding a new language means opening a new country. This one added Hungarian and reached the Hungarian chart within days. Top Paid charts in small countries have a low bar, a few sales a day can get you charted, and being charted brings store exposure in turn.

When to move: Tools like this aren't tied to a deadline, but the earlier you claim the local search terms for a given trade, the better. This one is already moving into German-speaking countries and the US. If the niche you're after happens to be cabinet hardware, it will most likely fill in more languages (inferred: Dutch and Nordic languages) before spring 2027.

What would show you got it wrong: ① This app never takes off in a big market like Germany (by 11-06 Germany had only 2 ratings and roughly 28 paid Utilities ranking), which would show the model only works where the paid-chart bar is low in small countries and there's no volume in bigger ones; ② after launch you find the target trade mostly uses Android and isn't used to paying for tools (check install counts of comparable paid tools on the local Play Store); ③ the hardware manufacturers release a free app that works across sizes and outputs cut lists and drill patterns.