Specificity is calculated by summing the weights of each part of the selector:
ID selectors contribute 1000, Class/Attribute/Pseudo-class selectors contribute 10,
Element/Pseudo-element selectors contribute 1. Inline styles have the highest weight (10000).
The Universal selector (*) contributes 0. The total specificity score determines which rule applies.
Selector Specificity Weight Breakdown
Selector Type
Weight Contribution
Example
Inline Style
10000
<div style="color: red;">
ID Selector
1000
#myElement
Class, Attribute, Pseudo-class
10
.my-class[data-attr]:hover
Element, Pseudo-element
1
div, p::before
Universal Selector (*)
0
*
What is CSS Selector Weight?
CSS Selector Weight, more accurately termed CSS Specificity, is the mechanism browsers use to determine which CSS rule declaration will be applied to an HTML element when multiple rules target the same element. In essence, it's a scoring system that assigns a numerical value to selectors based on their complexity and type. The rule with the highest specificity score wins and its styles are applied. Understanding CSS Selector Weight is crucial for any web developer aiming to create predictable, maintainable, and efficient stylesheets. It helps resolve conflicts, overrides, and ensures your intended styles are consistently rendered across different browsers and devices. Without a grasp of CSS Specificity, styles can appear to be ignored or overridden by seemingly less complex selectors, leading to frustration and debugging challenges. This calculator helps demystify that process by breaking down selector complexity into quantifiable values, making CSS Selector Weight calculations straightforward.
Who should use it:
Web Developers (front-end, full-stack)
CSS Preprocessor Users (Sass, Less)
UI/UX Designers who work with front-end code
Anyone learning or troubleshooting CSS
Common misconceptions:
"Later rules always win": While order *does* matter, it's only the tie-breaker. If an earlier rule has higher specificity, it will win regardless of its position.
"ID selectors are always the highest priority": Inline styles (style attribute) actually have higher specificity than any ID selector.
"All selectors are equal": This is false; the type of selector (ID, class, element) significantly impacts its weight.
"Specificity is only for complex projects": Even simple layouts can encounter specificity issues, especially when integrating third-party CSS or frameworks.
CSS Selector Weight Formula and Mathematical Explanation
The calculation of CSS Selector Weight (Specificity) isn't a single, simple formula but rather a multi-digit score where each digit represents a category of selector. The most common way to represent this is as a four-digit number (though technically it's a list of values), often visualized as (Inline, IDs, Classes/Attributes/Pseudo-classes, Elements/Pseudo-elements). The higher the value in each category, and importantly, the further to the left the non-zero digit is, the higher the specificity.
The formula, conceptually, is to sum the counts of each selector type:
Interpretation: This selector has a good specificity. It will likely override general button styles (like `button { … }`) but could be overridden by an inline style or a selector with more IDs.
Example 2: Overriding a Framework Style
Scenario: A CSS framework applies a base style to all `h2` elements, but you need a more specific style for a section title.
Framework Selector:h2
Your Selector:body #content article h2.section-title
Interpretation: Your selector (1031) has a significantly higher specificity than the framework's base `h2` selector (1). Your custom styles for `.section-title` will correctly override the generic `h2` style, demonstrating the power of targeted CSS Selector Weight.
How to Use This CSS Selector Weight Calculator
Identify Your Selector: Determine the exact CSS selector you are using or considering.
Count Selector Components: Based on the selector's syntax, count the number of ID selectors, class/attribute/pseudo-class selectors, and element/pseudo-element selectors.
Check for Special Cases: Note if the selector includes an inline style attribute or the universal selector.
Input Values: Enter the counts and selections into the corresponding fields of the calculator (ID Selectors, Class/Attribute/Pseudo-class Selectors, Element/Pseudo-element Selectors, Inline Style, Universal Selector).
Calculate: Click the "Calculate" button.
Read Results:
Main Result (Specificity Score): This is the primary numerical value representing the selector's overall weight. A higher number means higher priority.
Intermediate Values: These show the breakdown of the score (IDs, Classes, Elements, Inline). This is crucial for understanding *why* a selector has a certain weight.
Interpret: Compare the specificity score to other selectors targeting the same element. A selector with a higher score will override one with a lower score. If scores are equal, the later rule in the CSS source order wins.
Use "Copy Results": Click "Copy Results" to easily paste the key details into documentation or for sharing.
Reset: Use the "Reset" button to clear the fields and start a new calculation.
This tool is invaluable for debugging styling issues, planning your CSS architecture, and ensuring that important styles are not accidentally overridden by less significant ones.
Key Factors That Affect CSS Selector Weight Results
Several factors directly influence the specificity score of a CSS selector, impacting which styles ultimately get applied. Understanding these is key to mastering CSS:
Number of IDs: Each ID selector (`#main-nav`) adds a significant weight (1000 points). Selectors with multiple IDs are very specific. Use IDs sparingly as they are generally discouraged for styling due to their high specificity and single-element limitation.
Number of Classes, Attributes, and Pseudo-classes: These selectors (`.button`, `[type="submit"]`, `:hover`) each contribute 10 points. Combining them increases specificity substantially. This is the most common way to create specific selectors without resorting to IDs.
Number of Elements and Pseudo-elements: Basic element selectors (`div`, `p`) and pseudo-elements (`::before`, `::after`) each add 1 point. These form the base of most selectors but have the lowest contribution, making them easily overridden by more specific selectors.
Inline Styles: Styles applied directly to an HTML element via the `style` attribute (e.g., `
`) have the highest specificity (10000 points). They override almost all external or embedded stylesheet rules. Overuse can lead to unmaintainable code.
Universal Selector and Combinators: The universal selector (`*`) and combinators (space, `>`, `+`, `~`) have a specificity of 0. They don't add weight but are essential for grouping or defining relationships between selectors.
`!important` Declaration: While not part of the specificity calculation itself, `!important` overrides specificity entirely. A rule marked with `!important` will always take precedence over other rules, regardless of their specificity score. However, overuse of `!important` is considered bad practice and can make CSS debugging extremely difficult.
Browser Defaults/User Agent Stylesheets: These are the browser's built-in styles. They typically have the lowest specificity (often considered 0) and are easily overridden by any author-defined styles, including those with the lowest specificity like element selectors.
Frequently Asked Questions (FAQ)
Q: What is the difference between specificity and the order of CSS rules?
A: Specificity is the primary mechanism for determining which rule applies. If two rules have the *same* specificity score, then the rule that appears later in the CSS source order (or in the HTML if inline styles are used) will win.
Q: Can specificity be represented as a simple number?
A: It's often represented as a four-digit number (e.g., 0,2,1,0) where each digit corresponds to a category: Inline Styles, IDs, Classes/Attributes/Pseudo-classes, and Elements/Pseudo-elements. You compare the digits from left to right. For example, 0,1,0,0 (1 ID) is more specific than 0,0,10,0 (10 classes).
Q: When should I use IDs versus classes for styling?
A: Generally, use classes for styling. IDs have very high specificity and can only be applied to one element. Over-reliance on IDs for styling can lead to specificity wars. IDs are best reserved for JavaScript hooks or page anchors.
Q: Does nesting selectors in preprocessors like Sass increase specificity?
A: Yes, nesting selectors in Sass/Less often results in compound selectors (e.g., `nav ul li a`). Each part of the compound selector adds to the specificity score, increasing the overall weight compared to just `a`.
Q: How do I deal with specificity issues when using a CSS framework?
A: Frameworks often use high specificity selectors. To override them, you might need to use selectors with equal or higher specificity, or conditionally use `!important` as a last resort. Understanding the framework's selector patterns is key.
Q: What is the specificity of `::selection`?
A: Pseudo-elements like `::selection` are generally treated similarly to pseudo-classes in terms of specificity, contributing 10 points (like a class).
Q: How does specificity affect performance?
A: While not a direct performance bottleneck, overly complex selectors or frequent specificity overrides can increase the workload for the browser's rendering engine. Maintaining flatter, more manageable CSS with appropriate specificity leads to cleaner code and potentially faster rendering.
Q: Can I use the universal selector (*) to lower specificity?
A: The universal selector has a specificity of 0 and does not add to the score. It's often used in conjunction with other selectors (e.g., `ul li a`) or in resets (`* { margin: 0; padding: 0; }`) but doesn't inherently lower specificity on its own; it simply doesn't add to it.