Pixel / REM / EM Converter (CSS Units)

開発者文章

入力

自動処理

出力

クライアント側

Viewport Units

Viewport	vw	vh
360px (Mobile)
768px (Tablet)
1280px (Laptop)
1920px (Desktop)

Reference Table

ピクセル	REM	EM	PT
8px
10px
12px
14px
16px
18px
20px
24px
32px
48px
64px

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ガイド

Pixel / REM / EM Converter

Instantly convert between CSS units: pixels (px), root em (rem), and em. Adjust the base font size and watch all values update in real time. Perfect for front-end developers translating design specs into CSS.

使い方

Enter a value in any of the three unit fields — px, rem, or em — and the other two update instantly. Adjust the base font size (default 16px) using the slider or input field to match your project's root font size. The reference table below shows common conversions at a glance.

特徴

双方向変換 – Edit px, rem, or em and all others update instantly
Adjustable Base Font Size – Slider and input sync, default 16px
Reference Table – Common sizes auto-calculated for your base font size
Real-Time Updates – Throttled input for smooth performance
クライアントサイドのみ – No data sent to any server

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 よくある質問

What is the difference between rem and em in CSS?

rem (root em) is relative to the root element font size (html), making it consistent across the entire page. em is relative to the font size of the parent element, which can compound in nested elements. rem is generally preferred for layout consistency.
Why is 1rem equal to 16px by default?

Browsers set a default root font size of 16px unless overridden. So 1rem = 16px, 0.5rem = 8px, 1.5rem = 24px. If you set html { font-size: 62.5%; }, then 1rem = 10px, making math easier.
When should I use px instead of rem or em?

Use px for values that should not scale with user font preferences, like borders, shadows, or media query breakpoints. Use rem for font sizes and spacing so your layout respects the user's accessibility settings. Use em for component-relative sizing.
How does browser zoom affect CSS units?

Browser zoom scales all CSS units proportionally, including px. This is different from OS-level text scaling. However, if a user changes their browser default font size, rem and em values adjust while px values do not — making rem/em better for accessibility.