CSS logical properties describe layout relative to a component’s text and block flow: for example, margin-inline-start is the left margin in horizontal left-to-right text and the right margin in horizontal right-to-left text. Use them when a layout should adapt to writing direction or writing mode; keep physical properties when a design must stay attached to a particular screen edge.
What are CSS logical properties?
Physical properties name fixed edges or dimensions: left, top, width, and height. Logical properties name positions and sizes in the content’s flow: inline-start, inline-end, block-start, block-end, inline-size, and block-size.
The distinction is about intent, not just shorthand. A physical left always means the left edge. inline-start means the beginning of the text line, which can map to different physical edges depending on the writing context.
How do the block and inline axes work?
Inline follows the line; block follows the stacking direction
The inline axis runs in the direction text proceeds along a line. The block axis is perpendicular to it and follows the direction blocks stack. Neither axis is inherently horizontal or vertical.
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- In horizontal writing, the inline axis is horizontal and the block axis is vertical.
- In vertical writing, the inline axis is vertical and the block axis is horizontal.
Writing mode is more than left-to-right versus right-to-left
The mapping is shaped by writing-mode, direction, and text-orientation. Broadly, writing-mode sets block-flow direction, direction sets the inline base direction, and text-orientation affects glyph orientation. A logical property follows that writing context; it is not a permanent alias for a particular physical side.
For example, margin-inline-start maps to the left margin in horizontal LTR, the right margin in horizontal RTL, and can map to the top margin in a vertical writing mode. Use the axes to reason about the result rather than memorizing a fixed translation.
How do logical properties map to physical ones?
This table shows common mappings for horizontal writing. In vertical writing, the inline and block axes change physical orientation, so the corresponding sides change too.
| Flow-relative intent | Horizontal LTR | Horizontal RTL |
|---|---|---|
| Inline start | Left side | Right side |
| Inline end | Right side | Left side |
| Block start | Top side | Top side |
| Block end | Bottom side | Bottom side |
| Inline size | Extent along the horizontal text line | Extent along the horizontal text line |
| Block size | Extent perpendicular to the text line | Extent perpendicular to the text line |
Logical properties are available across several CSS families, not only spacing:
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- Spacing:
margin-inline-start,padding-block, and related longhands and axis shorthands. - Sizing:
inline-sizeandblock-size, along with their minimum and maximum variants. - Borders: logical border sides and border-radius properties.
- Positioning:
inset-inline-start,inset-block-end, and related inset properties. - Other flow-sensitive values: logical forms of
floatandclear, plus alignment values such asstartandend.
What is the difference between inline-size and width?
width and height describe physical dimensions. inline-size describes a size along the inline axis, while block-size describes one along the block axis. In horizontal writing, inline-size generally corresponds to width and block-size to height; when the writing mode is vertical, those axes switch physical orientation.
Choose based on the requirement. If a component should keep its size relationship to the text flow across writing modes, use the logical sizing property. If it must have a particular physical width or height regardless of writing mode, use width or height.
How do I replace margin-left with a logical property?
If the margin belongs at the beginning of the text line, replace margin-left with margin-inline-start. If it belongs at the end, use margin-inline-end. If it must remain on the physical left edge in every writing mode, keep margin-left.
For spacing on both sides of an axis, use margin-inline or margin-block. The same approach applies to padding and other properties that provide logical equivalents.
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Example: a flow-aware card
.card {
inline-size: min(100%, 42rem);
padding-block: 1rem;
padding-inline: 1.25rem;
margin-inline: auto;
border-inline-start: 0.25rem solid currentColor;
}The card’s size and spacing are expressed along the writing axes. Its start border is on the left in horizontal LTR and on the right in horizontal RTL. This example illustrates the mapping; it is not a browser test.
Example: positioning relative to flow
.badge {
position: absolute;
inset-block-start: 0.5rem;
inset-inline-end: 0.5rem;
}Here, the badge sits at the block-start and inline-end corners of its positioned containing block. Use top, right, bottom, or left instead when the position is intentionally tied to physical edges, such as a control that must remain at the viewport’s top-right corner.
Do CSS logical properties work with RTL?
Yes: logical properties express flow-relative intent, so inline-start and inline-end follow the inline direction. In horizontal RTL, inline-start is the right side and inline-end is the left. Block-start and block-end still describe the block axis, not the start and end of a text line.
Logical CSS does not, by itself, solve every bidirectional text-ordering issue. Set up text direction appropriately in the document and understand how direction participates in the writing-mode model; use logical properties for layout decisions that should follow that context.
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Do CSS logical properties work in vertical writing modes?
They are designed to express layout in terms of the writing axes, including vertical writing modes. In vertical writing, the inline axis becomes vertical and the block axis horizontal. As a result, an inline-start margin may map to a top margin rather than a left or right margin.
When designing for vertical text, determine which axis the requirement refers to first, then select the relevant logical property. Do not assume that “inline” means horizontal or that “block” means vertical.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What shorthand and cascade pitfalls should I watch for?
Four-value shorthands still use physical sides
margin: 1px 2px 3px 4px means top, right, bottom, left, in that order. The same physical-side model applies to four-value padding and border shorthands. These values do not become block-start, inline-end, block-end, and inline-start in RTL or vertical writing.
If the values are meant to follow flow, use logical longhands or logical axis shorthands such as margin-block and padding-inline.
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Mixed physical and logical declarations need deliberate cascade order
Corresponding physical and logical properties participate together in the cascade according to the element’s computed writing mode; they are not always independent settings. Changing the writing context can therefore change which physical side corresponds to a logical declaration.
When both forms appear in a rule set, check their order and the computed writing mode instead of assuming one declaration will affect only a separate side. Avoid mixing them casually, especially when a physical declaration is intended as a fallback.
Do not mechanically replace every left or right
A replacement is appropriate only when the layout intent is flow-relative. A fixed-position menu attached to the physical left edge, for example, may properly use left. A decorative border intended to mark the start of a reading line is a better fit for border-inline-start.
How should I choose between physical and logical properties?
- Choose a logical property when a position, spacing, size, border, or alignment should track the text or block flow.
- Choose a physical property when the requirement names a fixed screen or physical edge, or a physical width or height.
- For reusable components expected to appear in RTL or vertical writing, check each layout rule for hidden assumptions about left, right, width, and height.
- Review shorthands and mixed declarations during migration; changing a longhand alone may not make the whole rule flow-aware.
The W3C CSS Logical Properties and Values Level 1 document is a Working Draft dated 4 December 2025, not a final Recommendation. The documentation available for this guide does not establish a browser-version matrix, so check a current compatibility table before relying on a particular property in a specific support target.
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