# RPN 28x Calc — user reviews > 28 indexed App Store user reviews of RPN 28x Calc by tredje design, rated 5.00/5 from 33 ratings. - Source: https://appshunter.io/ios/app/rpn-28x-calc/id529927583/reviews - App overview in markdown: https://appshunter.io/ios/app/rpn-28x-calc/id529927583.md - Rating breakdown: 5★ 33 · 4★ 0 · 3★ 0 · 2★ 0 · 1★ 0 ## Newest reviews (14 of 28) ### 5/5 — Very nice recent update! *2021-04-14* This app has been living in my Home Screen for a long time because of how useful it is; and now it has complex numbers, user defined buttons, and linear regression! Thank you! ### 5/5 — A fantastic calculator *2021-02-14* I hope you continue to support this app! ### 5/5 — SUPERB *2021-01-22* I will no longer miss my venerable 28s ### 5/5 — Top notch *2021-01-09, version 3.2.1* I’ve tried most HP calculators on both android and iOS. This one is at top top of the list. Well done implementation that looks great and works well on both iPhone and iPad. Really nice on the larger iPhones. ### 5/5 — Great RPN calculator. *2020-08-15* Great calculator. ### 5/5 — Awesome RPN app !! *2020-04-30* Great app to replace my now not functioning m48+ emulator that let me going since my hp m48 went the way of the dodo. Wonderfully supported app that offers great features including hms+ hms- etc in an easy to use interface that offers the flexibility of being a fully fledged iOS app and not just an emulator!! ### 5/5 — Best RPN Calc I’ve tried by far *2020-04-02, version 3.1* I’m an old HP-28C junkie. My dad turned me on to HP calculators and RPN in the 80’s. For years I’ve been searching for a decent RPN calc for the iPhone/iPad. Prior to this, all the ones I’ve tried have been severely flawed. On some stack manipulation is wrong or weird — like not entering the current number in the stack twice if I hit enter twice. Infuriating. Alternatively people have made direct emulators of the old HP calculators —as though technology hasn’t gotten better since 1986. This app gets it just right. Everything I loved about my old HP, and everything good about modern tech. ### 5/5 — FANTASTIC - this is the only way... *2017-07-29* I can't really run a "normal" calculator because I've always used RPN, and it makes sense. Nothing else makes sense. So even when I got my iPad, I still pulled out my RPN calculator to add 2+2. Then I found this app! So happy, so perfect! I can hardly believe it - this is everything I want or need. PERFECTION! I'm so grateful I found this one because RPN is the only way to go, and this one works without the problems and weirdness of the other RPN app I tried. That other one was several times the price, and turned out to be a somewhat bizarre and terribly problematic nightmare, in my opinion. I deleted it very quickly. This one works. And, it is well designed, it has GREAT documentation, and I absolutely love it. This app is turning my physical RPN calculator into a museum piece lol. This is a great app, and they've made me a happy camper :) ### 5/5 — Just like an HP28S *2016-01-10* I used an HP 28S when I went to engineering school and I loved it. This app works almost exactly like my old HP. I love this app. ### 5/5 — The best HP emulator! *2014-10-06* Having tried three different HP-48 emulators and found all of them capable but lacking in various aspects, I am happy to say that this HP-28 emulator is sheer pleasure! The functionality is all there, the color and look of the original HP-28S is faithfully reproduced, the left hand side keyboard is very neatly implemented, easily slide between the trig/exp functions mode and alphanumeric, and I can program the various constants into alphanumeric combinations (e.g., ME for the electron mass, or h for Planck's constant). The stack is easily visible as a running tape, and most useful feature: You can scroll the stack and touch any stack entry to pick it out and put it on top of the stack. But most importantly, this emulator is a joy to use! I find myself coming back to it again and again to admire all the user-friendly features and just play with it. A fun calculator, and will probably only get better. ### 5/5 — Best calculator ever *2013-09-17, version 1.2* As a brokendown MIT grad, I can say that this is the answer to my prayers. ### 5/5 — Nice Job! *2013-05-04* The 28C was my first RPN calculator during my undergraduate degree. This app does a great job of emulating that experience. Thx much! ### 5/5 — Who'd have thought... *2013-04-08* Great surprise when searching for an RPN calculator application and running across this app which is reminiscent of my HP 28s from years past. Functions great for what I need it for, the adaptation for the IPad is great! Kudos to the author! ### 5/5 — Excellent RPN Calc *2013-01-05* Years ago I shed tears when my faithful Hp28s finally crunched its last number. Although this app differs In some ways, I think it combines the best of what I liked in my Hp28s, plus adds some very nice features being a touch interface. Well done. ## Most critical reviews (10 lowest-rated) ### 2/5 — HP 28S looks but *2016-07-02, version 2.2.1* This calculator has the looks of the great 28S but not all the functionalities. There is no symbolic calculations as in the real calculator. On the plus side, the stack operations are more functional than the real calculator. Hope they can add this powerful feature in latter versions. ### 4/5 — Powerful & Easy to Use *2017-04-22* If you're comfortable with rpn (reverse polish notation), this is an excellent app. It may be overkill for the average joe, but this is reminiscent of my 48GX calculator, used back in engineering school, without the graphics/plotting interface. If you're not accustomed to rpn calculators, but are in a technical field, now is the time to consider learning. There's no huge learning curve here; just a different way of entering your numbers. It seems awkward at first, but for large formula hacking, rpn is the way to go, making short work of the most complicated calculations! This one is more expandable than at first meets the eye, offering all the basic necessities for solid number crunching. ### 4/5 — Good app, some room for improvement *2015-08-16* Nice app, very accurate emulator, except for the fact that it doesn't support programming, which is still a major drawback. Once you add this functionality, you will see sales go up significantly **Developer response:** Thanks. Programming will be part of version 3.0. Beta-testing of that version is about to start. Let me know if you would like to participate (send me an email). ### 4/5 — Ahh, the memories *2013-05-11* In the olden days I had an hp 28s. I loved it and it was a great calculator at the time. This isn't a bad reproduction, but please keep working on it. ### 5/5 — Awesome!! *2025-09-26* I had the original physical model and this is a faithful experience and I greatly enjoy using it every day. The best calculator by far!! Amazing thank you!! ### 5/5 — Thank You *2024-09-20* While it doesn't do a couple of things my old 28s does, the extended UI functionality is exceptional. No other calculator replaces the 28S...I am almost always surrounded by computers and screens, but always reach for this app when maths needs to be done! Thank you for this effort...if I am ever in EU I will find you and buy you a beer! ### 5/5 — I've been looking for a calculator app like this *2024-04-04* I only recently discovered this app, so I'm just now digging into its very rich set of features. The Free42 & Plus42 calculators are amazing, but RPN 28x Calc shows what is possible when you ignore the "boundaries" that limit traditional calculators. I can't wait to learn more about this app, and really use it. ### 5/5 — No longer miss my 28S *2024-01-06* I’m so impressed with this calculator. Thanks for creating this! Great attention to detail on the user interface. ### 5/5 — My favorite Calc app and I’ve tried many *2024-01-05* I grew up using a real HP32, so perhaps I’m biased towards this interface, but I love using this calculator. It provides the best balance between being a traditional RPN calculator and maximizing the benefits of the smartphone I’ve seen. Most of the straight HP calculator emulators use the original display, which has, at most, 4 visible numbers in the stack. Why? That’s a silly limitation on a smartphone. This app also lets you do actual drag and drop on the stack so you don’t need to be adept at ROLL and ROLLD commands. Bonus binary conversions, etc. Most RPN calcs that aren’t based on an original HP architecture just don’t implement RPN well —including the “new” HP Prime (which I own and don’t consider a traditional HP). I encourage you to skim the manual. This app has so many features that you can get lost. I use, at most, 10% of the features, and would not have found my favorites by randomly pushing buttons. ### 5/5 — By far the best RPN calc for iOS *2022-10-29* As a recovering HP calculator user, I’m very picky with my calculator apps. However, this app checks all the boxes for me. It looks great, it has satisfying haptic feedback, charming optional key clicks, you can program custom buttons (log2 for me), and so on. I emailed the creator with some feedback, and they politely listened an eventually implemented the change. It even comes with a comprehensive manual! Probably a better manual than my HP 50g. Well worth the money, and clearly an app made with love. ## Most praised reviews (4 highest-rated) ### 5/5 — I don’t have enough nice things to say about how this works! *2022-06-08* I have tried several other RPN calculators (I have been an HP 28S user for nearly 30 years) And none of them work as nicely as this, this so closely and wonderfully expresses the awesomeness of the HP 28S and RPN. ### 5/5 — HP Calculator fan *2022-02-09* My electrical engineer dad gave me his HP 45 to use in middle school when he no longer needed it. As a birthday present from Service Merchandise, my parents gave me a new HP 41CV. It carried me through High School, College and Grad school. I still have it. The 41CV is in a safe place. The HP 28c/s came out in college but I couldn’t justify the cost. I have most of the HP emulators on my iPhone. This is by far my favorite. It utilizes the screen better then any other HP calculator app. It doesn’t over load the screen keys with too much information. It allows the alternative key functions to by swiped to become active. The user can select more easily the key needed. The colors of keys and output display are contrasting which makes using the calculator a joy. Haptic feed back is awesome too. Finally, a right swipe brings up a blank keyboard area you can populate with custom keys/variables/functions. This is the RPN calculator app HP would release. It is better then a physical calculator. It does not try to be a physical calculator it uses the strength of an iPhone/iPad screen to make it more usable and user friendly. You can’t go wrong with this app. Keep up the great work. ### 5/5 — A power-user delight! *2022-01-17* I use this calculator a lot when breadboarding circuits, and I’ve added a whole bunch of custom buttons tied to functions that calculate values related to the ICs I’m using, eg. voltage regulator feedback resistors, current setting resistors, “quick” filters, inductor/capacitor ripple, type II and III compensators, etc. It is a little marvel. Somehow, this button-based RPN interface really makes it work on a touch screen, whereas various other “mobile” interfaces that try and exploit fancier controls fall way short of the promise. This one has just the right mix of plain “buttonery” and screen gestures. I like it better than the thing it’s emulating. I know, what a travesty, but there you go. If only phone batteries lasted as long as calculator batteries. But as far as this app goes, it seems to do everything right and is a battery-miser. The rest is on Apple to improve :) ### 5/5 — Excellent Calculator *2021-12-17, version 3.4.1* If you are looking for an RPN calculator this is the one to get. Feels just like the original HP, however it’s always in your pocket! --- *Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-08-17.*