Line Height Calculator: Perfect Typography for Web & Mobile Design
A free online tool to calculate and convert line height values between different units (px, em, %, unitless) for optimal text readability across all devices.
Line Height Calculator
Calculate line height based on font size and vice versa
1.50
24px
150%
What is Line Height and Why is it Important?
Line height (also known as leading) is the vertical space between lines of text in a paragraph. It's a fundamental typographic property that significantly impacts readability, visual rhythm, and overall user experience.
Proper line height creates breathing room between text lines, making content easier to read and reducing eye strain. It's especially critical for:
- Long-form content where readers spend significant time
- Small text sizes that need additional spacing for clarity
- Responsive designs that work across multiple screen sizes
- Accessibility compliance for users with visual or cognitive impairments
- Maintaining consistent vertical rhythm in your design system
How Line Height is Calculated
Line height can be specified in several units, each with different behaviors:
Unitless Values (Recommended)
A multiplier of the font size (e.g., 1.5)
Example: If font-size is 16px and line-height is 1.5, the actual spacing will be 24px
line-height: 1.5;
Pixels (px)
Fixed height regardless of font size
Example: line-height: 24px will always be 24px regardless of font size
line-height: 24px;
Percentage (%)
Percentage of the font size
Example: If font-size is 16px and line-height is 150%, the spacing will be 24px
line-height: 150%;
Em/Rem
Relative to font size (em) or root font size (rem)
Example: 1.5em is 1.5 times the element's font size
line-height: 1.5em;
The Line Height Formula
The basic relationship between these units is:
- Unitless value = Line height in pixels ÷ Font size in pixels
- Percentage = Unitless value × 100
- Pixels = Font size × Unitless value
Best Practices for Line Height
Finding the perfect line height involves balancing several factors:
- Font size relationship: Smaller text generally needs more relative line height (1.5-1.6) while larger headings can use tighter spacing (1.1-1.3)
- Line length: Longer lines (more characters per line) benefit from increased line height
- Font characteristics: Fonts with larger x-heights need more line spacing
- Always use unitless values: They scale proportionally when font size changes
- Responsive adjustments: Consider slightly increasing line height on smaller screens
General Guidelines
- Body text: 1.4 to 1.6 times the font size
- Headings: 1.1 to 1.3 times the font size
- Form inputs: 1.4 to 1.5 times the font size
- Button text: 1 to 1.25 times the font size
Common Line Height Issues and Solutions
Text Appears Cramped
Lines of text are too close together, making reading difficult
Solution: Increase line height (try 1.5-1.6 for body text)
Text Feels Disconnected
Too much space between lines breaks the flow of reading
Solution: Decrease line height (1.3-1.4 may work better)
Inconsistent Spacing
Line height looks different across browsers or devices
Solution: Use unitless values instead of px or em
Vertical Alignment Issues
Text doesn't align properly with other elements
Solution: Use consistent line height values throughout your design system
Line Height Across Platforms
Different platforms handle line height in unique ways:
Web (CSS)
Supports unitless, px, em, rem, and percentage values
line-height: 1.5;
Flutter
Uses unitless height property in TextStyle
height: 1.5
iOS/SwiftUI
Uses lineSpacing for additional space
lineSpacing: 8
Our calculator helps you convert between these different systems, ensuring consistent typography across platforms.
How Our Line Height Calculator Helps
Our free line height calculator solves common typography challenges:
- Instant conversion: Quickly convert between unitless, pixel, and percentage values
- Real-time preview: See exactly how your text will look with different line height settings
- Cross-platform code: Get ready-to-use code for web (CSS, Tailwind) and mobile (Flutter) applications
- Interactive controls: Fine-tune your typography with precision sliders and inputs
- Responsive testing: Ensure your line height works across all screen sizes
- Dark mode support: Test your typography in both light and dark environments
Whether you're a designer creating a new design system, a developer implementing typography, or just someone who wants to improve text readability, our calculator provides the perfect solution for achieving professional typography.
Frequently Asked Questions
What is the ideal line height for body text?
For most body text (16px), a line height between 1.4 and 1.6 (22-26px) provides optimal readability. Longer lines of text benefit from values at the higher end of this range.
Should I use pixels or unitless values for line height?
Unitless values are recommended as they scale proportionally when font size changes. This creates more consistent typography across your application, especially in responsive designs.
How does line height affect accessibility?
Proper line height improves readability for all users, but it's especially important for those with dyslexia, visual impairments, or cognitive disabilities. WCAG 2.1 recommends line spacing of at least 1.5 within paragraphs.
Why does my text look different across browsers?
Browsers may render fonts slightly differently. Using unitless line height values helps maintain consistency. Also, be aware that some fonts have built-in line spacing that can affect the final appearance.
How do I implement line height in a design system?
Create a scale of line height values that correspond to your type scale. Typically, smaller text needs relatively more line height, while larger headings need less. Our calculator can help you determine these values.
Perfect Typography is Just a Click Away
Typography is a fundamental aspect of user experience design. With our line height calculator, you can ensure your text is not just legible, but truly readable and accessible across all platforms and devices.
Last updated: December 12, 2025