減らす vs. 減る: The Difference You Need to Know for JLPT N3

Introduction

減らす (herasu / to reduce) and 減る (heru / to decrease) are two Japanese verbs that often confuse learners.

Both are connected with the idea of something becoming smaller in number, amount, or degree.

For example, both verbs can be used when talking about body weight:

「体重を減らす」
Reduce your weight.

「体重が減る」
Your weight decreases.

The basic idea looks very similar, but the way the two verbs describe the situation is different.

Once you understand this difference, choosing the right verb becomes much easier in everyday Japanese and in JLPT vocabulary and reading questions.

Let’s start with the most important rule.

The Short Answer

「減らす」(herasu) means to make something smaller or fewer.

「減る」(heru) means that something becomes smaller or fewer.

An easy way to remember the difference is:

• 減らす → 少なくする (sukunaku suru / make something less)
• 減る → 少なくなる (sukunaku naru / become less)

Compare these two sentences:

「食べる量を減らす。」
Reduce the amount you eat.

Here, someone intentionally makes the amount smaller.

「食べる量が減る。」
The amount you eat decreases.

Here, the amount itself becomes smaller.

The key difference is therefore:

• 減らす → make less
• 減る → become less

Understanding the Difference

減らす: Someone Makes Something Smaller

減らす (herasu / to reduce) is commonly used when a person, company, organization, or other agent causes something to become smaller in number or amount.

For example:

「毎月の出費を減らす。」
Reduce monthly expenses.

The expenses do not simply decrease by themselves. Someone takes action, such as spending less money, to reduce them.

Other common combinations include:

• 仕事を減らす
  reduce the amount of work

• 食事の量を減らす
  reduce the amount of food

• ミスを減らす
  reduce mistakes

• 電気の使用量を減らす
  reduce electricity consumption

• ゴミを減らす
  reduce waste

A useful question is:

“What is someone trying to make smaller?”

You will often see the particle を before 減らす.

「量を減らす」
Reduce the amount.

減る: Something Becomes Smaller

減る (heru / to decrease) describes a change in which the number, amount, or degree of something becomes smaller.

For example:

「最近、客の数が減った。」
The number of customers has decreased recently.

This sentence focuses on the change in the number of customers. It does not mean that someone intentionally reduced the number of customers.

Other common combinations include:

• 人口が減る
  the population decreases

• 体重が減る
  weight decreases

• 仕事が減る
  the amount of work decreases

• 売り上げが減る
  sales decrease

• 水が減る
  the amount of water decreases

A useful question is:

“What is becoming smaller?”

You will often see the particle が before 減る.

「量が減る」
The amount decreases.

When Are They Used?

減らす and 減る are both very common in everyday conversation, business Japanese, news reports, and JLPT reading passages.

Everyday Conversation

They are frequently used when talking about health, diet, work, or daily habits.

「少し体重を減らしたいです。」
I want to lose a little weight.

The speaker wants to take action to make their weight lower, so 減らす is used.

Compare:

「最近、体重が減りました。」
I’ve lost weight recently.

Here, the speaker is describing the result: their weight has become lower.

Business Japanese

These verbs often appear when discussing expenses, sales, working hours, and productivity.

「会社は経費を減らす必要があります。」
The company needs to reduce its expenses.

The company intentionally wants to make its expenses lower.

「今年は売り上げが減りました。」
Sales decreased this year.

Here, the sentence simply describes a decrease in sales.

News and JLPT Reading

These verbs also frequently appear in texts about population, environmental problems, production, accidents, and social trends.

「この地域では若い人の人口が減っている。」
The population of young people in this area is decreasing.

「政府は交通事故を減らすため、新しい対策を始めた。」
The government introduced new measures to reduce traffic accidents.

It is common to see both 減らす and 減る in the same reading passage, so understanding the difference is important for JLPT reading comprehension.

Check the Difference with Examples

Examples with 減らす

「健康のために、砂糖の量を減らしています。」
I am reducing the amount of sugar I consume for my health.

The person intentionally uses less sugar, so 減らす is appropriate.

「会社は電気代を減らすために、新しい設備を導入しました。」
The company introduced new equipment to reduce its electricity costs.

The company is taking action to make the electricity costs lower.

「仕事が忙しすぎるので、来月から仕事の量を減らします。」
I’m too busy, so I will reduce my workload starting next month.

Someone intentionally changes the amount of work.

「ミスを減らすために、作業の手順を見直しました。」
We reviewed the work procedures in order to reduce mistakes.

Reducing the number of mistakes is the goal, so 減らす is used.

Examples with 減る

「毎日運動していたら、体重が3キロ減りました。」
After exercising every day, I lost three kilograms.

The body weight became lower as a result of exercising.

「この町では、子どもの数が年々減っています。」
The number of children in this town is decreasing every year.

The sentence describes a continuing change in the number of children.

「冬になると、この店のお客さんが減ります。」
The number of customers at this store decreases in winter.

The number of customers becomes smaller during winter.

「最近は仕事が減って、少し時間に余裕ができました。」
Recently, I have had less work, so I have a little more free time.

The amount of work has become smaller.

Common Mistakes

One of the most common mistakes is mixing up を and が.

For example:

「ダイエットをして体重を減りました。」

This is unnatural.

減る describes something becoming smaller, so the natural sentence is:

「ダイエットをして体重が減りました。」
I went on a diet and lost weight.

If you want to focus on intentionally reducing your weight, you can say:

「ダイエットをして体重を減らしました。」
I went on a diet and reduced my weight.

Compare the two:

「体重が減りました。」
My weight decreased.

This focuses on the change or result.

「体重を減らしました。」
I reduced my weight.

This focuses more on the person intentionally causing the change.

Here is another common mistake:

「会社は残業時間が減らしました。」

This is unnatural.

Because the company intentionally reduced overtime hours, use を:

「会社は残業時間を減らしました。」
The company reduced overtime hours.

But this sentence is also natural:

「会社の残業時間が減りました。」
The company’s overtime hours decreased.

Here, the sentence describes the result rather than the action.

How to Tell Them Apart on the JLPT

When you are deciding between 減らす and 減る on the JLPT, first check the particle and the meaning of the whole sentence.

If the sentence means that someone makes something smaller, 減らす is usually the correct choice.

If something itself becomes smaller, 減る is usually the correct choice.

For example:

「健康のために、毎日の食事の量を＿＿＿ことにした。」
For my health, I decided to reduce the amount I eat every day.

The sentence contains:

「食事の量を」
the amount of food + を

The person intentionally makes the amount smaller, so the answer is:

「減らす」

Now look at this example:

「この町では、ここ10年間で人口が大きく＿＿＿。」
In this town, the population has significantly decreased over the past ten years.

The sentence contains:

「人口が」
the population + が

The population itself became smaller, so the natural answer is:

「減った」

When you are unsure, ask yourself these two questions:

• Is someone intentionally making something smaller? → 減らす
• Is a number or amount becoming smaller? → 減る

Expressions such as 「ために」(tame ni / in order to) followed by an action or measure often appear with 減らす.

For example:

「事故を減らすために、交通ルールを厳しくする。」
Traffic rules will be made stricter in order to reduce accidents.

On the other hand, expressions that describe changes over time often appear with 減る, such as:

• 以前と比べて
  compared with before

• 年々
  year by year

• 最近
  recently

• この10年間で
  over the past ten years

These expressions are clues that the sentence may be describing something becoming less rather than someone intentionally reducing it.

Summary

The basic difference between 減らす and 減る is simple:

• 減らす (herasu) → someone makes something smaller
• 減る (heru) → something becomes smaller

It is especially useful to remember these two patterns together:

「量を減らす」
reduce the amount

「量が減る」
the amount decreases

Instead of memorizing only the dictionary meanings, pay attention to を and が, and ask whether the meaning is “make less” or “become less.”

Small differences like this are important on the JLPT. They can affect not only vocabulary questions but also your understanding of reading passages.

RJT (Rapid Japanese Training) helps you practice these easily confused Japanese expressions through JLPT-style questions. By answering questions repeatedly, you can move beyond simply knowing the meaning and learn to choose the right expression naturally.

If you often think, “I know what both words mean, but I still choose the wrong one in a test,” try practicing them in real question formats.

RJT (Rapid Japanese Training)でJLPT問題に挑戦する