Best free unit converter apps for Android (2026)

Unit converter apps on Android range from "perfect" to "ad-clogged hellscape." Here's what to look for and which features actually matter for daily use.

Short answer: the best free unit converter app for Android is one that works offline, covers at least length, weight, volume, temperature, area, speed, data and fuel economy, has a calculator built in, and asks for no permissions it does not need. Our pick is All-in-1 Converter Calculator (free, ad-supported, no account). If you only convert once in a while, you may not need an app at all — see the built-in options below.

Converter options on Android compared

How to check a converter app in two minutes

1. On its Google Play page, open Data safety and check what it collects and shares. A converter should not need your contacts, precise location or microphone.
2. Look for the Contains ads and In-app purchases labels under the app name, so you know the business model before you install.
3. Turn on airplane mode and convert something. If it stops working, it is not offline.
4. Test three known answers: 1 inch = 2.54 cm exactly, 1 lb = 0.45359237 kg exactly (both defined by the 1959 international yard and pound agreement), and 100 °C = 212 °F.
5. Check the categories you need are free rather than behind a subscription.

What makes a good converter app

• Offline: works on a plane, in a basement, in a tunnel
• Wide unit coverage: length, weight, volume, temperature, area, speed, time, data, fuel economy at minimum
• Built-in calculator: for follow-on math without app switching
• Fast launch: < 2 seconds to first conversion
• Minimal ads: banner is fine, full-screen interstitials kill it
• Free with no subscription paywall on basic features

Red flags

• Permissions for contacts, location, microphone (why?)
• Forced signup
• Subscription required to use more than 3 unit categories
• Conversions wrong by > 0.5% (yes, this happens)

Categories worth having

• Length (inches ↔ cm, miles ↔ km, etc.)
• Weight (lb ↔ kg, oz ↔ g)
• Volume (cups ↔ ml, gallons ↔ liters)
• Temperature (°F ↔ °C ↔ K)
• Area (sq ft ↔ sq m, acre ↔ hectare)
• Speed (mph ↔ kph ↔ m/s)
• Data (MB ↔ GB ↔ TB)
• Fuel economy (mpg ↔ L/100km)

Bonus: kitchen-aware volume

Generic volume converters fail with ingredients because density varies. If you bake or cook from gram-based recipes, pair a generic converter with an ingredient-aware tool such as a flour grams-to-cups converter, which uses the weight of a cup of that ingredient rather than water.

On iPhone and the web too

All-in-1 Converter Calculator is now available on the Apple App Store and as a web app at allinoneconvertertool.com, so the same offline-friendly unit coverage works across iOS, Android, and any browser.

On a desktop instead of a phone? An image downloader extension for Chrome saves web images as JPG or PNG without a separate converter.