Make sense
of the measure.

Four instruments. Free to explore.

Volume, length, mass and temperature have their own illustrated instruments. Each follows the same converted quantity as the numerical answer.

The instruments illustrate entered quantities. They do not measure a real object, sense temperature, or make the screen a physical ruler. The vessel’s capacity and scale are shown. Reduce Motion keeps the presentation still.

Getting started

1. Convert: choose Volume, Length, Mass or Temp, or open All categories. Select the source and destination units and enter a value. Copy result copies the answer; equivalent results let you choose another destination.
2. Lab: try the worked examples. Metron Pro enables the full expression editor, dimensional checking, uncertainty calculations and molar-mass workflow.
3. Library: find your favourites, saved setups and custom units. Open History to revisit saved conversions, or Constants to browse and copy the CODATA 2022 values.
4. Settings and Membership: use the controls at the top of Convert, or the Settings button in Library. Membership shows the available plans, restore and Apple’s subscription-management sheet.

All 138 standard categories and 1,307 shipped units are free. The numerical engine works at full precision; display precision and some workflow tools depend on your plan. Conversions and constants work offline. Purchases, restoration and iCloud synchronization need Apple’s services.

Metron Pro

Pro adds the expression editor with compound units, significant-figure and uncertainty tools, constants inside calculations, molar mass from chemical formulae, unlimited saved history and favourites, saved conversion setups, custom units, CSV/LaTeX/Markdown result exports and optional private iCloud sync.

Free access includes all four instruments, every standard unit, constants browsing, the basic widgets and Shortcuts actions, five favourites, limited history, and full personal backup and restore. Metron does not request or display advertising.

Plans, trials and billing

Choose Monthly or Annual, or the one-time Lifetime purchase. Membership obtains the localized total price and billing period from the App Store. The annual plan offers a three-day free trial only where Apple confirms eligibility; the purchase screen states the annual price first, then the terms that apply to you. Monthly has no free trial.

Subscriptions renew automatically unless cancelled. Apple charges the displayed price according to the purchase confirmation. After an eligible free trial, the annual subscription renews at the displayed annual price unless cancelled before it ends. For a free or discounted trial, Apple recommends cancelling at least 24 hours before the trial ends. Apple’s cancellation instructions explain how to manage your subscription.

Lifetime is one payment and does not renew. Buying Lifetime does not cancel a subscription you already have. Use Manage or Cancel Subscription in Membership to review any separate subscription. A cancelled subscription keeps its verified access until the expiry shown by Apple; unavailable renewal information is labelled as unavailable.

To recover access after reinstalling or changing devices, sign in to the App Store with the purchasing Apple Account and choose Restore Purchases. No Metron account is required. Purchases are governed by Apple’s Standard EULA.

Keep your work

Saved setups and custom units

A saved setup keeps its title, input, source and destination units, and display preferences. Opening it calculates the result again. Custom units use a positive finite factor against a standard unit in the same category—for example, a personal flask defined in millilitres. Offset temperatures and logarithmic units cannot be reference units.

Backup and restore

Open Library → Backup and restore, then choose Export full backup or Restore from backup. A backup includes history, favourites, custom units, saved setups and display preferences. It excludes purchases and iCloud account/opt-in state.

Backup export and restore are limited to 20 MB and 50,000 total records per file. If your data exceeds either limit, export is unavailable; your saved records are not deleted.

Restore previews the record counts, existing IDs, conflicts and references needing repair. It adds new records while preserving existing records with the same ID, including conflicts. Restoring display preferences is optional. The backup file is readable by anyone who has access to it, so choose its storage or sharing destination carefully.

Optional iCloud sync

Pro users can turn on iCloud sync in Settings and confirm a merge with the current iCloud account. The app then uses your private iCloud database for records and iCloud key-value storage for supported settings. The displayed status distinguishes configuration, observed operations and errors. “iCloud is configured” does not mean every device has finished syncing; an operation can remain pending while offline or while Apple’s service is unavailable. Synchronization is not an independent backup.

Turning sync off stops settings synchronization and requests local record storage. On iOS and iPadOS versions earlier than 26, you must fully close and reopen Metron to apply a storage change after your records are saved. Newer versions may also need a restart; follow the status shown in the app. Editing pauses while a restart is required, and you can export a recovery backup. Pending iCloud transfers may continue until the app is fully closed. Changing iCloud accounts clears the app’s opt-in and requires a new merge confirmation. Existing local records remain available when Pro expires or sync is turned off; neither action automatically erases previous iCloud copies.

What happens when I reach a free limit?

Existing records are preserved. New conversion history stops saving when the free allowance of ten unpinned conversion entries is reached; you can remove entries or choose Pro to save more. Existing setups and custom-unit definitions remain readable and included in backups after Pro expires. Creating or editing them requires Pro.

Help with a result or purchase

A result looks wrong

Check the selected unit variant, especially US/imperial gallons, short/long/metric tons and absolute temperatures versus temperature intervals. Open a result’s unit definition to inspect its relation and source. If the result still looks wrong, send us the input, both units, expected answer and reference you used.

The scene is still or has a different scale

Reduce Motion, Low Power Mode, editing and available screen space affect the illustration. Very large or signed quantities may use a schematic view. The numerical answer remains the result to read and copy.

Prices or a renewal date are unavailable

Check your connection and Apple Account, then retry loading plans or use Restore Purchases. Membership does not substitute a guessed price or date. If payment is pending approval, access updates when Apple reports the verified purchase.

A storage warning appears

Read the status shown in the app. “Restart to apply this change” means your records were saved; fully close and reopen Metron to apply the storage change. If recent edits could not be saved, editing pauses and the unsaved records stay in the open session. Use Retry storage or Export recovery backup before closing the app. A recovery file preserves a separate copy; normal restore keeps existing records when their IDs conflict. Your saved store is kept rather than reset.

Contact support

Email mwsupplylimited@gmail.com with your device model, iOS/iPadOS version, Metron version and steps to reproduce. Include only the records or screenshots you want us to receive. We do not need your Apple Account password or payment-card details.

Read how the app handles your information in the Privacy Policy.