Hapi vs PlantCalculator
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
Hapi
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OUR STORY Hapi started with something I have always loved: numbers. I use a calculator all the time, and I have always enjoyed playing with numbers and finding little reasons to make math more fun. One day, I thought: what if a calculator could make people smile too? So I started playing with the idea. A few experiments turned into funny sounds, unexpected reactions, and eventually Hapi. What started as a simple idea to make math a little more fun became something much more entertaining than I expected. Sometimes, even a calculator can have a personality. HOW IT WORKS Pick a theme and start calculating. Every number key shows its own picture, displays its name and plays its own sound. WHAT YOU CAN DO • Add, subtract, multiply, divide and work with percentages • Hear a different sound on every key • See a picture and a name on every number • Watch confetti burst when you press equals • See your full calculation above the result • Switch themes with one tap • Turn sounds on or off at any time • Use Hapi in many languages GREAT FOR Quick daily math, checking a bill, or a little fun with sounds. FREE VERSION • Music and Animals themes • The full calculator with sounds and confetti • No ads of any kind PREMIUM • Extra Premium themes • New themes added from time to time Themes are updated from time to time. Some themes stay for a while and then make room for new ones. You can choose a monthly subscription, a yearly subscription or a one-time Lifetime purchase. The yearly subscription starts with a 14-day free trial. After the trial, it renews automatically at the yearly price unless you cancel at least 24 hours before the trial ends. You can manage or cancel it in your App Store account settings. This is always your choice. MADE BY AN INDEPENDENT DEVELOPER Hapi is made with care by an independent developer in İzmir, Turkey. PRIVACY Hapi uses Firebase Analytics and Crashlytics to understand how the app is used and to fix crashes. Hapi does not need an account. Terms of Use (EULA): https://www.apple.com/legal/internet-services/itunes/dev/stdeula/
PlantCalculator
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The nameplate reads "52.7 kg/cm²G." Your reference is in psi. The formula wants MPa. You can stop doing that conversion in your head. Plant Calculator brings together the calculations used every day in refinery and chemical plant equipment inspection — one app, built for the field. ■ Type the number on the nameplate, as-is Every input field has a unit selector. Enter kg/cm²G, psi or bar exactly as written, and the app does the conversion. If you think in kg/cm², set it as your default in Settings and every screen opens that way. 15 categories, 65 units. ■ Works where there's no signal Inside a vessel, inside a tank — every calculation runs entirely on your device. ■ Enter only what you already know - Pick a nominal size and schedule, and OD and wall are filled in (ASME/JIS, 45 sizes) - Pick a material and temperature, and the allowable stress is interpolated and filled in (9 materials) No more flipping through dimension tables. ■ Main features - Quick Check: from pipe and inspection data, review original wall, required thickness, corrosion rate, remaining life and thickness margin together - Required thickness: minimum wall for piping and pressure vessels under internal pressure (JIS B 8265 / High Pressure Gas (KHK), ASME Sec.VIII Div.1, ASME B31.3; cylinders, heads, straight pipe and elbows) - Corrosion rate & remaining life from previous/current thickness and elapsed years - Metal loss check: average, minimum and variation from readings, with simplified general and local metal-loss checks - Vertical tower check: internal pressure, dead weight, wind and seismic (static seismic coefficient method); checks tension and compression for operating and shutdown cases and shows a reference thickness. Skirt included - External pressure: simplified allowable external pressure check for cylinders - Nozzle reinforcement: area replacement method - Relief valve sizing: required orifice area based on API 520 - Piping: support span, pressure drop and velocity - Vessel: flange, bolt torque, flat plate, cone and support loads - Surface area: outer area of pipe, elbow, head and reducer; add count and insulation thickness for painting/cladding area and a material estimate - Tank / line totals: connect elements to sum area, volume and weight - Thermal expansion from temperature difference - Calculator + equation solver: scientific calculator (trigonometry, logs, powers, roots, memory, EE input, DEG/RAD) that also solves simultaneous equations in x, y and z - Unit conversion: 15 categories, including multiplication and division with units (e.g. 200 mm × 200 mm = 0.04 m²) - Size quick reference: NPS to OD, wall, ID, volume and pipe weight - Pipe dimension lookup: pick a size to see OD and wall per schedule (ASME B36.10M/B36.19M / JIS, physical dimension reference values) - Flange rating check: enter the rated pressure from your standard and compare with design pressure (ASME B16.5, etc.; rating table not bundled) - Material list: temperature-dependent allowable stress reference values (based on High Pressure Gas example standards) - Glossary for inspection and design terms - Calculation history: save, delete and copy as CSV - 8 languages (Japanese, English, Español, Português, 한국어, Deutsch, العربية, Русский), dark mode ■ Important This app is a supporting tool for design and inspection. Formulas are representative, and allowable stresses, dimensions and ratings are approximate reference values. Always verify against the official formulas and latest values of the applicable codes (JIS B 8265 / High Pressure Gas example standards / ASME Sec.II Part D / B16.5 / B36.10M, etc.) before making any decision. Do not rely on this app's results alone.
Screenshots
Verdict
The clearest difference is in-app purchases: PlantCalculator at none against Hapi's 3. PlantCalculator also leads on iOS requirement (13.0 vs 15.0). Hapi's advantage is ads (none vs shown). On price, update cadence and device support there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Both are free to download. Hapi sells 3 in-app purchases, starting at $1.99 per month. PlantCalculator asks for nothing beyond the download.
Hapi ships an update every 2 weeks, PlantCalculator every 9 days. Both last shipped on November 5, 2026.
| Parameter | Hapi | PlantCalculator |
|---|---|---|
| Price | Free | Free |
| Update frequency | Every 2 weeks | Every 9 days — better |
| Ads | No — better | Yes |
| In-app purchases | Yes | No — better |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Requires iOS | 15.0 | 13.0 — better |
| Further details — not scored | ||
| Size | 17 MB | 25 MB |
| Age rating | 4+ | 4+ |
| Developer | LedaPremium | Ryo Iida |
In-app purchases
Hapi
- HaPi Premium Monthly$1.991 Month
- HaPi Premium Yearly14 Days trial$9.991 Year
- HaPi Premium$19.99
PlantCalculator
No in-app purchases









