A1 noun Neutral #2,705 most common

半径

hankei /haŋkeː/

The distance from the center of a circle to its outer edge. It is half of the diameter and is used in both mathematical contexts and to describe a physical area around a specific point.

Examples

3 of 5
1

この公園は半径1キロ以内にあります。

This park is within a one-kilometer radius.

2

円の半径を計算してください。

Please calculate the radius of the circle.

3

俺の生活半径、最近すごく狭いんだ。

My living radius has been really small lately.

Word Family

Noun
半径
Related
直径
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Memory Tip

The first kanji '半' (han) means 'half'. Think of it as 'half' of the path (径) across the circle.

Quick Quiz

この円の直径は10センチなので、_____は5センチです。

Correct!

The correct answer is: a

Examples

1

この公園は半径1キロ以内にあります。

everyday

This park is within a one-kilometer radius.

2

円の半径を計算してください。

formal

Please calculate the radius of the circle.

3

俺の生活半径、最近すごく狭いんだ。

informal

My living radius has been really small lately.

4

半径が2倍になると、円の面積は4倍になる。

academic

When the radius doubles, the area of the circle quadruples.

5

駅を中心に半径500メートルのエリアを調査します。

business

We will survey the area within a 500-meter radius centered on the station.

Word Family

Noun
半径
Related
直径

Common Collocations

半径を測る to measure the radius
半径5メートル a 5-meter radius
行動半径 range of action / activity radius
半径を伸ばす to extend the radius
有効半径 effective radius

Common Phrases

半径5メートルの幸福

Happiness within a 5-meter radius (finding joy in immediate surroundings)

生活半径

one's daily living sphere

行動半径が広い

to have a wide range of activity

Often Confused With

半径 vs 直径

Chokkei (diameter) is the full width of the circle passing through the center, while hankei is only half of that.

📝

Usage Notes

While primarily a math term, it is very commonly used in daily conversation to talk about how far one travels or the area around a home/station.

⚠️

Common Mistakes

Learners often confuse the kanji for 'half' (半) and 'flat' (平), or mix up the reading with 'chokkei' (diameter).

💡

Memory Tip

The first kanji '半' (han) means 'half'. Think of it as 'half' of the path (径) across the circle.

📖

Word Origin

A Sino-Japanese compound of '半' (half) and '径' (path/diameter).

Grammar Patterns

Noun + の + 半径 (Radius of...) 半径 + Number + Unit (A radius of X units)
🌍

Cultural Context

The phrase 'radius of 5 meters' is often used in Japanese media to describe the personal, intimate space of one's direct social circle.

Quick Quiz

この円の直径は10センチなので、_____は5センチです。

Correct!

The correct answer is: a

Related Words

協力

A1

Cooperation or collaboration where two or more people combine their efforts to achieve a common goal. It is used in both personal and professional settings to describe working together as a team or providing assistance.

提案

A1

A suggestion or proposal of a plan or idea for others to consider. It is used in both casual conversations and professional meetings to introduce a potential course of action.

輸出

A1

The act of sending goods or services produced in one country to another country for sale or trade. In Japanese, it functions as a noun and a suru-verb, representing the 'exit' of products from a domestic market.

輸入

A1

The act of bringing goods, services, or materials into a country from abroad for sale or use. In Japanese, it functions as a noun or can be combined with 'suru' to become a verb meaning 'to import'.

資源

A1

Shigen refers to valuable materials or assets, such as natural minerals, energy sources, or human talent, that can be used for production or survival. It is widely used in economics, environmental science, and daily life to describe both raw materials and abstract wealth.

保護

A1

The act of keeping someone or something safe from harm, damage, or loss by providing care or creating boundaries. It is a versatile term in Japanese used for social welfare, environmental conservation, and digital security.

観察

A1

Observation is the act of watching someone or something carefully in order to gain information or understand a process. It is frequently used in scientific studies, nature analysis, and describing the act of paying close attention to details.

競争

A1

Kyousou refers to the act of competing or vying with others to achieve a goal, win a prize, or establish superiority. It is a versatile term used in sports, business, and academics to describe both structured contests and general rivalry.

拡大

A1

The act of making something larger in size, scale, or scope. It is frequently used for physical enlargement (like a photo) or abstract growth (like a business or a problem).

製造

A1

The process of making or producing goods, typically on a large scale using machinery. It refers specifically to industrial manufacturing rather than making things by hand on a small scale.

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