Units of Measurement
Converting customary, metric, and cross-system units, plus elapsed time.
This page is a free outline of what the Units of Measurement lesson covers — it is not the lesson itself. The interactive lesson, practice, quizzes, and AI Tutor are inside the app.
This lesson covers
- Choosing Appropriate Units Choosing appropriate units means picking a size that fits what you’re measuring — millimeters for a coin’s thickness, kilometers for a highway — so the number is sensible.
- Time and Elapsed Time Elapsed time is how long something lasts — the gap from a start time to an end time — found by subtracting, borrowing 60 minutes from an hour when needed.
- Unit Conversion – Between Systems Switching between customary and metric uses approximate factors (usually given in the problem), like 1 inch ≈ 2.54 cm or 1 mile ≈ 1.609 km.
- Unit Conversion – Customary Converting within the U.S. customary system uses fixed factors you memorize — 12 inches = 1 foot, 16 ounces = 1 pound, 4 quarts = 1 gallon — multiplying or dividing to switch units.
- Unit Conversion – Metric The metric system is built on powers of 10, so you convert by moving the decimal: 1 km = 1,000 m, 1 m = 100 cm, 1 L = 1,000 mL, 1 kg = 1,000 g.
- Unit Conversion – Temperature Temperature converts between Fahrenheit and Celsius with two formulas: C = (F − 32) × 5/9 and F = C × 9/5 + 32.
Hover or tap a dotted ⓘ concept for a quick definition.
Inside the app, Units of Measurement comes with:
Read the explanation here for free — then practice it for real, with everything you need in one place.
24/7 AI Tutor — Ask anything and get a step-by-step explanation when you’re stuck — it teaches the concept, not just the answer. Every answer verified by three independent AIs.
- Practice sets — Open-book practice questions at your level, easiest-first — as many as you want, never scored.
- Quizzes — Scored quizzes on the whole lesson, so you know when you’re ready to move on.
- Skills Check — A concept-by-concept map of what you’ve mastered and what to focus on next.
- Worked examples — Tap the Brain Button on any example for alternative step-by-step explanations.
- Glossary — Plain-English definitions of every key term in the lesson.
- Formula sheet — The GED® & HiSET® formula sheets, on screen while you practice.
- Practice calculator — An on-screen calculator to build your calculator skills before test day.
- Math-fact flashcards — Quick drills for addition, multiplication, perfect squares, and square roots.
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