Element.getBoundingClientRect() already accounts for CSS zoom. Use its left, top, width, and height as viewport-relative CSS-pixel values; do not multiply them by the zoom factor again. To express the same point in document coordinates, add window.scrollX and window.scrollY. “Screen coordinates” can also mean browser-window or physical display pixels, which require a separate, platform-specific conversion.
What getBoundingClientRect() returns under CSS zoom
A call to element.getBoundingClientRect() returns a DOMRect describing the element’s rendered border box. The rectangle includes padding and borders, is relative to the viewport’s top-left corner, and uses CSS pixels. CSSOM View specifies that rectangle APIs return scaled lengths, so CSS zoom is already reflected in every rectangle edge and dimension.
Consequently, this is correct:
const rect = element.getBoundingClientRect();
const viewportLeft = rect.left;
const viewportTop = rect.top;
const viewportRight = rect.right;
const viewportBottom = rect.bottom;
const viewportWidth = rect.width;
const viewportHeight = rect.height;This is not correct:
const rect = element.getBoundingClientRect();
const zoom = 2;
const wrongLeft = rect.left * zoom;
const wrongWidth = rect.width * zoom;Multiplying the rectangle again double-counts CSS zoom and moves the result too far. A zoom value of 1 (or 100%) is normal size; 2 (or 200%) magnifies the rendered page, while values below 1 reduce it.
Choose the coordinate system before writing code
The phrase “screen coordinates” is ambiguous. Decide which origin and unit your consumer expects, then keep every measurement in that same system.
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| Coordinate space | Origin and unit | How to obtain it | Typical use |
|---|---|---|---|
| Viewport | Top-left of the current layout viewport; CSS pixels | Use rect.left and rect.top directly |
Fixed overlays, hit regions, alignment with viewport-based UI |
| Document (page) | Top-left of the document; CSS pixels | Add window.scrollX and window.scrollY |
Absolute page coordinates and scroll-independent annotations |
| Visual viewport | The portion currently visible on a mobile device; CSS pixels | Inspect window.visualViewport |
Pinch zoom, browser UI movement, or an on-screen keyboard |
| Browser-window or physical display | Window or hardware-display origin; platform-dependent units | No universal formula is established by these DOM APIs | Operating-system automation and native integrations |
A DOMRect is therefore not automatically a hardware “screen-pixel” rectangle. Browser-window placement, device-pixel ratio, page zoom, and visual-viewport state can all affect a conversion to display pixels. Define the target browser and operating system, and validate that conversion in the environment where it will run.
Convert viewport coordinates to document coordinates
Scrolling changes a fixed element’s viewport-relative rectangle because the viewport origin stays put while the document moves. Add the current page offsets to change the origin to the document:
function getDocumentRect(element) {
const rect = element.getBoundingClientRect();
return {
left: rect.left + window.scrollX,
top: rect.top + window.scrollY,
right: rect.right + window.scrollX,
bottom: rect.bottom + window.scrollY,
width: rect.width,
height: rect.height
};
}
const target = document.querySelector('.target');
const pageRect = getDocumentRect(target);
console.log(pageRect.left, pageRect.top);The width and height do not need a scroll adjustment: scrolling changes position, not the element’s dimensions. This conversion still produces CSS pixels; it does not convert to device or operating-system pixels.
Position an overlay without double-scaling
Overlay fixed to the viewport
Use the rectangle directly when the overlay is position: fixed. Both the rectangle and the overlay use the viewport as their origin.
const target = document.querySelector('.target');
const overlay = document.querySelector('.overlay');
const rect = target.getBoundingClientRect();
overlay.style.position = 'fixed';
overlay.style.left = `${rect.left}px`;
overlay.style.top = `${rect.bottom}px`;
overlay.style.width = `${rect.width}px`;Overlay positioned in document space
For an absolutely positioned overlay whose containing block is the document, add the scroll offsets. Make sure the overlay’s containing block really uses the document origin; a positioned ancestor can establish a different origin.
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const rect = target.getBoundingClientRect();
const left = rect.left + window.scrollX;
const top = rect.top + window.scrollY;
overlay.style.position = 'absolute';
overlay.style.left = `${left}px`;
overlay.style.top = `${top}px`;Recalculate after scrolling, resizing, content changes, or any style change that affects layout. A previously returned rectangle represents the geometry at the time you read it, not a permanently tracked point.
CSS zoom versus transform: scale()
CSS zoom and transform: scale() are not interchangeable. CSS zoom participates in layout, so surrounding flow and rendered geometry are affected. A scale transform visually scales an element without recalculating layout in the same way. Code that assumes one behavior can be wrong when the page uses the other.
.zoomed-panel {
zoom: 1.5;
}
.transformed-panel {
transform: scale(1.5);
transform-origin: top left;
}In both cases, read the actual rendered rectangle rather than attempting to infer it from a CSS declaration. If a component can use either technique, test its positioning and hit testing with each implementation.
Why offsetWidth and clientWidth may disagree
Rectangle APIs include CSS zoom, while client properties, offset properties, and scrolling APIs do not include it in the same way. For example, rect.width can differ from element.offsetWidth when an ancestor or the element itself is zoomed. Do not mix those values as though they share a unit without an intentional conversion.
Element.currentCSSZoom reports the effective CSS zoom, including zoom values inherited through ancestors. An ancestor at 2 and another at 3 produce an effective value of 6. It is useful for diagnosing why unzoomed measurements differ, but it is not a multiplier for getBoundingClientRect() output.
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const rect = element.getBoundingClientRect();
const effectiveZoom = element.currentCSSZoom;
console.log({
renderedWidth: rect.width,
effectiveZoom
});MDN labels currentCSSZoom newly available since March 2026. Check your supported-browser matrix before relying on it; the rectangle itself remains the primary measurement.
Mobile pinch zoom and the visual viewport
On mobile, the layout viewport and the visual viewport can diverge. Pinch zoom, the on-screen keyboard, and browser interface changes can shrink or move the area the user currently sees. When the job is to follow that visible area, inspect window.visualViewport rather than treating CSS zoom as a visual-viewport multiplier.
function reportViewports() {
const layoutWidth = document.documentElement.clientWidth;
const layoutHeight = document.documentElement.clientHeight;
const visual = window.visualViewport;
console.log({
layoutWidth,
layoutHeight,
visualLeft: visual ? visual.offsetLeft : 0,
visualTop: visual ? visual.offsetTop : 0,
visualWidth: visual ? visual.width : layoutWidth,
visualHeight: visual ? visual.height : layoutHeight,
visualScale: visual ? visual.scale : 1
});
}
reportViewports();
window.visualViewport?.addEventListener('resize', reportViewports);
window.visualViewport?.addEventListener('scroll', reportViewports);visualViewport.scale describes visual-viewport scaling; it is not a value to multiply into a DOMRect that already contains CSS zoom. Keep layout-viewport, visual-viewport, and document coordinates distinct.
Complete JavaScript helper
The following helper returns both common CSS-pixel spaces and makes the origin explicit.
export function measureElement(element) {
if (!(element instanceof Element)) {
throw new TypeError('Expected a DOM Element');
}
const rect = element.getBoundingClientRect();
return {
viewport: {
left: rect.left,
top: rect.top,
right: rect.right,
bottom: rect.bottom,
width: rect.width,
height: rect.height
},
document: {
left: rect.left + window.scrollX,
top: rect.top + window.scrollY,
right: rect.right + window.scrollX,
bottom: rect.bottom + window.scrollY,
width: rect.width,
height: rect.height
},
cssZoom: 'currentCSSZoom' in element ? element.currentCSSZoom : undefined
};
}
const measured = measureElement(document.querySelector('.target'));
console.log(measured);Keep the returned values as numbers until the final CSS assignment. Preserve fractional values unless your target API explicitly requires integers; rounding early can create visible one-pixel drift at non-integer zoom levels.
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Equivalent requests from cURL, Python, and Node.js
If you are implementing the browser code in a page, the JavaScript examples above are sufficient. For tooling that injects JavaScript into a browser, the same measurement logic can be evaluated after the page has reached the layout state you need. The following snippets show the core expression in each common environment.
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cURL with an automated browser endpoint
curl -X POST https://example.invalid/evaluate
-H 'Content-Type: application/json'
-d '{"script":"const r=document.querySelector(".target").getBoundingClientRect(); return {left:r.left,top:r.top,width:r.width,height:r.height};"}'The endpoint, authentication, and request format are provider-specific; the important part is that the script runs in the page and reads the rectangle without applying another zoom multiplier.
Python
from selenium import webdriver
from selenium.webdriver.common.by import By
with webdriver.Chrome() as driver:
driver.get('https://example.com')
result = driver.execute_script("""
const r = document.querySelector('.target').getBoundingClientRect();
return {left: r.left, top: r.top, width: r.width, height: r.height};
""")
print(result)Node.js
import { chromium } from 'playwright';
const browser = await chromium.launch();
const page = await browser.newPage();
await page.goto('https://example.com');
const result = await page.locator('.target').evaluate((element) => {
const r = element.getBoundingClientRect();
return { left: r.left, top: r.top, width: r.width, height: r.height };
});
console.log(result);
await browser.close();Troubleshooting coordinate mismatches
Everything is offset by the zoom factor
Cause: the rectangle was multiplied by zoom or currentCSSZoom. Fix: remove that multiplication and use rect.left, rect.top, and rect.width directly.
The overlay moves when the page scrolls
Cause: viewport coordinates were assigned to an absolutely positioned element, or document coordinates were assigned to a fixed element. Fix: pair viewport values with position: fixed; add scroll offsets for document-positioned elements.
Width differs from offsetWidth
Cause: those APIs do not report CSS zoom in the same way. Fix: choose one measurement family for the calculation, or document and intentionally convert between the two.
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It works on desktop but not during mobile pinch zoom
Cause: the visual viewport has moved or resized independently of the layout viewport. Fix: read window.visualViewport and listen for its resize and scroll events when tracking what is visible.
Values are correct initially but stale later
Cause: layout, scrolling, fonts, or responsive styles changed after the measurement. Fix: measure after the relevant layout is ready and recalculate on the changes that can move the target. In animation loops, batch reads before writes to avoid unnecessary layout work.
A conversion to monitor pixels is inconsistent
Cause: “screen” was treated as a single universal coordinate space. Fix: specify whether the consumer expects viewport CSS pixels, document CSS pixels, browser-window coordinates, or physical display pixels, then test the platform-specific conversion.
Performance and reliability checklist
- Read the rectangle after the target exists and its styles have been applied.
- Use one coordinate origin throughout each calculation.
- Do not mix
getBoundingClientRect()with offset, client, or scroll measurements without accounting for their different zoom behavior. - Keep fractional CSS-pixel values until the final rendering or input boundary.
- Re-read after scroll, resize, responsive-layout changes, or content changes that affect geometry.
- For mobile visibility, observe the visual viewport separately from CSS zoom.
- Test any browser-window or hardware-pixel conversion on the exact browser and operating system you support.
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cURL
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Python
import requests
r = requests.get("https://api.screenshotneo.com/v1/shot", params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"}, timeout=90)
open("shot.webp", "wb").write(r.content)Node.js
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Frequently Asked Questions
Why can rectangle values contain decimals?
CSS layout permits fractional CSS-pixel positions and sizes, especially with non-integer zoom or responsive calculations. Keep the decimals for alignment and round only at an API boundary that requires integers.
Can a DOMRect be passed directly to an operating-system mouse API?
Usually not. A DOMRect is viewport-relative CSS geometry; native mouse APIs commonly require browser-window or physical-display coordinates. The conversion depends on the browser, window placement, display scale, and device state, so define and test that mapping separately.
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