The best unit converter app depends on what you convert. For the widest range, Convert Any Unit Lite on iPhone covers more than 6,400 units in 51 categories, with ads. For a free Android converter with no ads at all, Converter NOW is open source. For everyday metric, imperial and kitchen conversions that work with no signal, Convert Units Calculator is free with one banner ad. And if you only convert now and then, the converter already built into your phone or search engine may be all you need.
Every app below was checked against its current App Store or F-Droid listing in September 2026. Prices, ratings and features change, so check the listing before you pay for anything.
Unit converter apps compared #
| App | Platforms | Range | Currency | Ads | Paid options |
|---|---|---|---|---|---|
| Convert Units Calculator | iOS, Android | 140 units, 19 categories (v1.0.5) | No, by design | One banner | Optional one-time upgrade |
| Convert Any Unit Lite | iPhone | 6,400+ units, 51 categories | Yes | Yes | None needed |
| Units – Pro Unit Converter | iPhone, iPad, Mac | 800+ units, 43 categories | Yes, 88 currencies | No | Tip jar |
| Unit Converter – Convert all | iPhone, iPad, Mac, Watch | 18+ categories | Yes, live | Yes | Subscriptions and one-time |
| Unit Converter – Pro Units App | iPhone | 16 categories (4 free) | Yes, 148 currencies | No | $2.99 one-time |
| Unit Converter – Scientific | iPhone | 1,000+ units, 80+ converters | Not listed | No | Optional tips |
| Converter NOW | Android, web, desktop | 200+ units, 30+ categories | Yes, needs internet | No | Free, open source |
| Google Search / iPhone Calculator | Built in | Common units | Yes | Search ads | Free |
What makes a unit converter app good? #
Most converters get the easy stuff right. Here’s what separates them:
- Exact factors. Since 1959 the inch has been exactly 2.54 cm and the pound exactly 0.45359237 kg (NIST SP 811). A quick test: convert 1 US gallon to liters. A good app shows 3.785412 (or more digits of 3.785411784).
- US and UK units kept apart. An imperial gallon is 20% bigger than a US gallon. An app that only offers “gallon” is guessing which one you mean.
- Speed. Results that update as you type, without a Convert button, save more time than any extra category.
- Offline use. Physical units never change, so they shouldn’t need a connection. Currency is the exception.
- A fair business model. Some apps lock basic categories behind a purchase or put a subscription screen in front of the first launch. Others show ads and collect data for them. Know which you’re choosing.
The apps in detail #
Convert Units Calculator: best for everyday and kitchen conversions offline #
Convert Units Calculator is our app, so weigh this entry accordingly. It’s built around one screen: type a number, and the answer appears large at the top with every other unit in the category worked out below it. Version 1.0.5 covers 140 units in 19 categories, from length, weight and temperature to fuel economy, torque and bandwidth, and it keeps US and UK gallons, pints and fluid ounces separate. Its Cooking category converts cups and spoons to grams for 26 ingredients, which most general converters can’t do. Every conversion runs on the device from exact factors, and there’s no account or sign-in.
The limits are real. There’s no currency converter, deliberately, because rates go stale. At 140 units it’s far smaller than the apps that list hundreds or thousands, so it won’t have obscure engineering or historical units, and it has no clothing or shoe sizes. It’s free with a single banner ad, and its site lists an optional one-time Convert Pro upgrade that removes the ad. The 19-category version is 1.0.5. Earlier builds had ten categories, so check the version number on your store listing.
Convert Any Unit Lite: most units, type-to-search #
Cider Software’s app lists over 6,400 units in 51 categories, including specialist ones like blood glucose and radiation dose. Its best idea is the input: you start typing a unit name without picking a category first, and it suggests matches. It shows the conversion formula with results, supports bookmarks, and has a 4.7 rating from about 48,000 reviews.
It’s ad-supported, and its App Store privacy label says it collects location, identifiers and usage data for third-party advertising and analytics. If that bothers you, pick one of the ad-free apps.
Units – Pro Unit Converter: large range without ads #
Homegrown Software’s app covers 43 categories and more than 800 units, with currency conversion across 88 currencies updated daily, and lets you hide units and reorder categories. Version 3.0 removed the ads and made the former premium features free, replacing them with an optional tip jar. The last update was in May 2024, and it has a 3.6 rating from 161 reviews, so it’s less actively maintained than some.
Unit Converter – Convert all: most features, most upsells #
oWorld Software’s app offers 18+ categories, offline conversion for physical units, live currency and crypto rates, a built-in calculator, cooking measurements, and clothing and shoe sizes. It’s well rated (4.6 from about 14,000 reviews). The catch is the monetization: it contains ads and sells a range of subscriptions and one-time purchases, including a $19.99 yearly Pro option. Good if you want everything in one app, and wrong for anyone who dislikes upsell screens.
Unit Converter – Pro Units App: pay once, no ads #
Tue Nguyen Minh’s app has 16 categories, including cooking, shoe sizes and currency (148 currencies). It has no ads and works offline. Only four categories are free, and a one-time $2.99 purchase opens the other twelve, so treat it as a paid app with a free trial.
Unit Converter – Scientific: engineering units, no ads #
A small, newer app from Ahmet Burak Albayrak with more than 1,000 units across 80+ converters, including engineering and scientific units. It’s ad-free, works offline for standard conversions, and its listing says it collects no data. The optional in-app purchases are tips. It has only a handful of ratings so far, so it’s less tested by the crowd.
Converter NOW: best free option on Android #
Damiano Ferrari’s Converter NOW is open source under the GPL, available on Google Play and F-Droid, and also runs on the web, Linux and Windows. It covers 200+ units in 30+ categories, including currency, has a built-in calculator and lets you reorder or hide units. It has no ads and doesn’t collect data. F-Droid flags that currency conversion depends on a network service, and that’s the only reason it asks for internet access.
The converter you already have #
Google Search has a unit converter built in: search “unit converter” or just type “5 km in miles”. Google’s help page lists temperature, length, mass, speed, volume, area, fuel consumption and currency among its categories. It needs a connection, though, and you get search ads around it.
The iPhone Calculator app can convert units and currency too. Apple’s user guide covers it under Convert units or currency in Calculator. It’s the quickest option if you already have Calculator open, and we compare it with a dedicated app in iPhone Calculator unit conversion vs a converter app. For more options beyond Google, see Google unit converter alternatives.
Which unit converter app should you pick? #
- You want every unit that exists: Convert Any Unit Lite, if you can live with ads.
- You want no ads and no payment: Converter NOW on Android, or Units – Pro Unit Converter on iPhone.
- You want currency too: Unit Converter – Convert all, Units – Pro Unit Converter, or Converter NOW, all with a connection.
- You cook from recipes in cups and grams: Convert Units Calculator’s Cooking category, or a dedicated kitchen app from our best cooking conversion app roundup.
- You travel or work without signal: any app that computes on the device. Our offline unit converter comparison shows which ones.
- You convert twice a month: Google or your phone’s calculator. No download needed.
Frequently asked questions #
What is the most accurate unit converter app? #
Any converter that uses the exact definitions (1 inch = 2.54 cm, 1 lb = 0.45359237 kg, 1 US gallon = 3.785411784 L) will give correct answers. The differences between apps are in how many decimals they show and whether they separate US and UK units. Test an app by converting 1 gallon to liters and 1 mile to kilometers (1.609344).
Is there a unit converter app without ads? #
Yes. Converter NOW (Android), Units – Pro Unit Converter (iPhone) and Unit Converter – Scientific (iPhone) have no ads. Unit Converter – Pro Units App has no ads but charges $2.99 for most of its categories.
Can my phone convert units without an app? #
Yes. Google Search converts units in any browser, and the iPhone Calculator app has a convert feature. Both are fine for occasional use. A dedicated app is faster if you convert often, and some work without a connection.
Do unit converter apps convert currency? #
Many do, but currency always needs an internet connection to fetch current rates. Some apps, including Convert Units Calculator, leave currency out so the whole app works offline with no stale numbers.
Are free unit converter apps safe? #
Most are, but free apps usually pay for themselves with ads, and ad networks may collect identifiers. Check the App Privacy section on the App Store or the Data safety section on Google Play before installing.