Weight conversion (g ↔ kg)

1Summary 重點摘要

1 kg = 1000 g, same as capacity.

2Vocabulary cards Vocabulary

3Step by step Steps

1. Step 1: The main rate1 kg = 1000 g is the fixed link between kilograms and grams; memorise this one line and every weight conversion has a basis. Kilograms measure heavier items, such as a 5 kg bag of rice; grams measure lighter items, such as a 2 g nail. The two units differ by exactly 1000 times, so every conversion is simply a multiply or a divide by 1000. A common mistake is remembering the rate as 100 or 10000, which shifts the answer by a whole decimal place, so always confirm the rate of 1000 before working.
2. Step 2: Big to small (× 1000)Kilograms to grams multiplies by 1000: 1.2 kg = 1.2 × 1000 = 1200 g, the decimal point moving three places right. Why multiply? Because grams are the smaller unit, so the same item must give a larger number; 1.2 kg can never equal 120 g. The rule reads: the unit shrinks and the number grows, matching capacity conversion, so the two topics confirm each other. A common slip is reversing the direction and writing 0.0012 kg; after finishing, check that the new number is larger to catch the mistake at once.
3. Step 3: Small to big (÷ 1000)Grams to kilograms divides by 1000: 4500 g = 4500 ÷ 1000 = 4.5 kg, the point moving three places left. The direction is the opposite: the larger unit gives a smaller number, so 4500 g becomes only 4.5 kg. The motto is big-to-small multiplies, small-to-big divides, and keeping these two lines in mind stops every reversal. The usual error is moving too few places, such as writing 45 kg for 4500 g; checking with 45 × 1000 = 45000, which does not match the original, exposes the slip immediately.
4. Step 4: Small values tooValues under a kilogram follow the same method: 80 g = 80 ÷ 1000 = 0.08 kg, moving three places left and padding zeros, treating 80 as 0080 first. Everyday anchors build the feel for size: an apple of about 200 g is 0.2 kg, and an eraser of about 20 g is 0.02 kg. A common mistake is padding too few zeros and writing 0.8 kg, moving only two places; remember that grams-to-kilograms gives less than 1 unless the grams exceed 1000, which is a quick check on the answer.
5. Step 5: Unify before addingQuantities in different units cannot be added directly: for 2 kg + 500 g, turn 2 kg into 2000 g first, then add, 2000 + 500 = 2500 g, which is 2.5 kg. The reason is that kilograms and grams differ by 1000 times, so adding 2 and 500 directly gives a meaningless 502. Unifying the units is the fixed first step for mixed-unit questions. The common error is forgetting to unify and obtaining an unreasonable 502 kg; a quick sense estimate of the real weight reveals the mistake.
6. Step 6: Everyday anchorsKeeping everyday weights in mind makes estimating and converting surer: an apple about 200 g, a 5 kg bag of rice equal to 5000 g, a newborn baby about 3 kg, a P6 pupil about 40 kg, and a lorry load measured in tonnes with 1 tonne = 1000 kg. With these anchors an unreasonable answer stands out at once, such as an apple of 2 kg. The common fault is lacking a feel for size, so a correct-looking calculation hides an absurd result; make a rough estimate a habit after every answer.

4Diagrams Diagrams

5Worked example Example

6Common mistakes Mistakes

7Quick check Quick check

8Recap Recap

• 1 kg = 1000 g
• kg → g multiply by 1000; g → kg divide by 1000
• Shift the point three places: 1.2 kg = 1200 g
• Unify units before comparing or adding
• Everyday anchors: apple 200 g, rice bag 5 kg