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RenjiCalc
Microwave Heating Time Calculator & Timer (iPhone)
Optimize convenience-meal and frozen-food heating time for your own microwave

"6 minutes at 500W"
for your microwave.

"6 minutes at 500W... what about my 800W microwave?" Get the answer instantly.
Watt conversion to timer start, all in one smooth flow.

  • Watt conversion
  • One tap from history
  • Live Activities support
  • Multiple microwaves
RenjiCalc screenshot

Easy watt conversion

Enter the original wattage and time, and instantly get the right time for your microwave.

One-tap timer from history

Pick frequently heated items from history and skip recalculating each time.

Progress on lock screen

Live Activities support lets you check remaining time on Dynamic Island and the lock screen.

Register multiple microwaves

Switch between multiple wattage presets such as home and office microwaves.

Reduce overheating mistakes

Use precise numbers instead of guesswork to avoid over- and under-heating.

Lightweight and fast

Focused features keep the flow from input to calculation to timer start fast and simple.

How to use (30 seconds)

  1. Enter the package wattage and heating time
  2. Select your microwave wattage
  3. Check the result and start the timer
Recommended for
- People who often eat frozen food or convenience meals
- People using 700W/800W or higher microwaves
- People who want fewer heating mistakes

FAQ

How is the time calculated when wattage is different?

The app converts time so the delivered energy stays equivalent, meaning time changes inversely with wattage.

What can I do with Live Activities (Dynamic Island)?

After starting the timer, you can monitor remaining time and progress on the lock screen and Dynamic Island.