ZAP!TIME

Microwave Calculators

Three free tools: convert cooking times between wattages, see what your microwave costs versus an oven, and pick the right capacity, power and turntable size.

Tool 1

Wattage time converter

Look for "output" or "cooking power" on the label or manual.

minutes · seconds

–
Tool 2

Energy cost: microwave vs oven

Electrical draw on the label; usually 1.4–1.7× the cooking watts.

Same meal in an electric oven

Microwave cost per month (daily use)–
Microwave cost per year (daily use)–
One meal – microwave–
One meal – oven–
Saved per year by using the microwave–
Tool 3

Size & wattage picker

Recommended capacity–
Recommended power–
Minimum turntable diameter–
Minimum cavity width–

Microwave buying & cooking guide

A microwave heats food by making water molecules vibrate with radio waves, so it is fast and energy-efficient for small portions. The three calculators above answer the questions people ask most: how long to cook, how much it costs and which model to buy.

Why wattage changes cooking time

Package directions assume a specific power, often 1,000–1,200 W. A 700 W unit delivers less energy per second, so the same food needs longer. As a close approximation, time scales in inverse proportion to power: a 3 minute recipe for 1,100 W needs about 4 minutes 20 seconds at 800 W. Always check early, stir or turn the food, and let it stand – standing time lets heat spread through the food.

Microwave sizes

CapacityTypical use
0.7 – 0.9 cu ft (20–25 L)Single person, dorm or office; reheating
1.0 – 1.4 cu ft (28–40 L)Couples and small families
1.5 – 2.2 cu ft (42–62 L)Families, large plates, casserole dishes

Countertop, over-the-range or built-in?

Countertop models are the cheapest and easiest to replace. Over-the-range models save counter space and include a vent fan, but their ventilation is usually weaker than a dedicated hood. Built-in and drawer models give a clean look but cost more and need professional installation. Measure the opening and add clearance for ventilation on every side as the manual requires.

Features worth paying for

  • Inverter technology gives steady low power instead of pulsing on and off, so food heats more evenly.
  • Sensor cooking adjusts time based on steam released by the food.
  • Combination modes add grill or convection for browning.
  • Easy-clean interior – ceramic or stainless enamel resists stains.

Safety basics

  • Never run an empty microwave and never use metal containers unless the manual allows it.
  • Use microwave-safe dishes and vent covers to avoid pressure build-up.
  • Stir liquids and let them rest to avoid superheating.
  • Stand food for the time recommended to avoid hot spots.

Frequently asked questions

Is the time conversion exact?

No. It is a good approximation for wattage differences up to about 30 %. For larger differences, cook in short steps and check the food.

Do microwaves use a lot of electricity?

They draw high power but only for a few minutes, so per meal they usually use much less energy than heating a full-size oven.

What wattage is best?

1,000–1,100 W suits most households. Higher wattage cooks faster but may need more care to avoid uneven heating.

How do I find my microwave's cooking wattage?

Check the label inside the door or the manual. If it only lists input power, assume the cooking power is about 60–70 % of it.