{"id":8240,"date":"2026-08-01T08:05:17","date_gmt":"2026-08-01T08:05:17","guid":{"rendered":"https:\/\/dextora.agency\/insights\/website-speed-on-low-end-devices-guide\/"},"modified":"2026-08-01T08:39:53","modified_gmt":"2026-08-01T08:39:53","slug":"website-speed-on-low-end-devices-guide","status":"publish","type":"insight","link":"https:\/\/dextora.agency\/en\/insights\/website-speed-on-low-end-devices-guide\/","title":{"rendered":"Speed on Low-End Devices: Why Your Site Is Only Fast for You"},"content":{"rendered":"<p>The most common sentence in any conversation about speed: &#8220;it opens instantly for me&#8221;. It is usually true and usually means nothing, because it was said by someone with a new computer, a wired connection and the site already in their browser cache.<\/p>\n<p>Real visitors are in different conditions, and that is where the money is lost.<\/p>\n<h2>Why developers do not see the problem<\/h2>\n<table>\n<thead>\n<tr>\n<th>Factor<\/th>\n<th>Development conditions<\/th>\n<th>A real visitor<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Device<\/td>\n<td>A powerful laptop<\/td>\n<td>A three or four year old phone<\/td>\n<\/tr>\n<tr>\n<td>Network<\/td>\n<td>Stable and wired<\/td>\n<td>Mobile, often unstable<\/td>\n<\/tr>\n<tr>\n<td>Cache<\/td>\n<td>Everything already loaded<\/td>\n<td>First visit, empty cache<\/td>\n<\/tr>\n<tr>\n<td>Distance to server<\/td>\n<td>Possibly nearby<\/td>\n<td>Another city or country<\/td>\n<\/tr>\n<tr>\n<td>Background<\/td>\n<td>Only the browser<\/td>\n<td>A dozen apps, low battery<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>Each row multiplies the others. Combined, what opens in a second for a developer takes five to eight for a visitor.<\/p>\n<h2>What actually slows things down on weak hardware<\/h2>\n<p>It matters to separate two different constraints: the network and the processor. The first is fixed by reducing weight, the second by reducing work.<\/p>\n<ul>\n<li><strong>JavaScript.<\/strong> The main culprit. A 300 kilobyte file downloads in a second but takes several times longer to parse and execute on a weak phone than on a computer. That is not about the network, that is about the processor.<\/li>\n<li><strong>Fonts.<\/strong> Every weight is a separate file. Four weights in two styles means eight downloads before text appears.<\/li>\n<li><strong>Unadapted images.<\/strong> A 2000 pixel wide image on a 360 pixel screen downloads in full and is then scaled, spending both bandwidth and memory.<\/li>\n<li><strong>Third-party scripts.<\/strong> Each is a separate connection to someone else&#8217;s server, whose speed you do not control.<\/li>\n<li><strong>Complex <a href=\"https:\/\/dextora.agency\/en\/insights\/microanimations-when-they-help-and-when-they-hurt-guide\/\">animation<\/a>.<\/strong> What is smooth on a computer stutters on a budget phone if the animated properties force layout recalculation.<\/li>\n<\/ul>\n<h2>How to test without buying a phone<\/h2>\n<p>You do not need to buy an old device, browser developer tools are enough:<\/p>\n<ol>\n<li>Open developer tools, the network tab.<\/li>\n<li>Enable throttling at the level of a slow mobile connection.<\/li>\n<li>In the performance tab, enable CPU slowdown of four to six times.<\/li>\n<li>Make sure to tick disable cache.<\/li>\n<li>Reload the page and watch the clock.<\/li>\n<\/ol>\n<p>This roughly corresponds to a mid-range phone from three years ago on an unstable connection. The difference from what you saw before is usually unpleasant.<\/p>\n<p>A second, even simpler check: take your phone, turn off Wi-Fi and open the site over mobile data somewhere outdoors, not in the office.<\/p>\n<h2>What to fix first<\/h2>\n<p>Ordered by result relative to effort:<\/p>\n<ol>\n<li><strong><a href=\"https:\/\/dextora.agency\/en\/insights\/core-web-vitals-speed-competitive-advantage\/\">Server response time<\/a>.<\/strong> If it exceeds a second, nothing else matters. This is the first thing to check and the most common real problem.<\/li>\n<li><strong>Unnecessary third-party scripts.<\/strong> Count them and remove those with no answer to what they are for.<\/li>\n<li><strong>Images.<\/strong> Modern format, dimensions matched to the actual screen, width and height always declared.<\/li>\n<li><strong>Fonts.<\/strong> Two weights instead of eight, with text displayed immediately.<\/li>\n<li><strong>JavaScript.<\/strong> Defer everything not needed for the first screen.<\/li>\n<li><strong>Animation.<\/strong> Opacity and transforms only.<\/li>\n<\/ol>\n<p>The first three usually deliver most of the result and require no rebuilding of the site.<\/p>\n<h2>A performance budget<\/h2>\n<p>The most effective tool available, and almost nobody uses it. The idea is simple: agree in advance on limits the page does not exceed.<\/p>\n<table>\n<thead>\n<tr>\n<th>Metric<\/th>\n<th>Working limit<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Server response<\/td>\n<td>under 200 ms<\/td>\n<\/tr>\n<tr>\n<td>Total page weight<\/td>\n<td>under 1 MB<\/td>\n<\/tr>\n<tr>\n<td>A single image<\/td>\n<td>under 300 KB<\/td>\n<\/tr>\n<tr>\n<td>Third-party scripts<\/td>\n<td>no more than 5<\/td>\n<\/tr>\n<tr>\n<td>Font files<\/td>\n<td>no more than 3<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>The value of a budget lies not in the numbers themselves but in turning &#8220;shall we add another widget&#8221; from a question of taste into a question of arithmetic. If a new tool does not fit within the limit, something has to go.<\/p>\n<h2>Why this matters commercially<\/h2>\n<p>The audience with weak devices and poor connections is not a marginal group. These are people travelling, on public transport, outside cities, on budget phones. In many niches they make up the majority of mobile traffic.<\/p>\n<p>And crucially: those people do not write to support saying &#8220;your site is slow&#8221;. They simply close the tab, and in analytics that looks like an ordinary bounce. Which is why the problem stays unnoticed for years, it produces no signal except a number that is easy to attribute to something else.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Five conditions developers test in and nobody else experiences. What actually slows things on weak hardware, how to reproduce those conditions in a minute without buying a phone, and why you need a performance budget.<\/p>\n","protected":false},"author":5,"featured_media":8236,"template":"","insight_category":[154],"insight_tag":[170,178,162],"class_list":["post-8240","insight","type-insight","status-publish","has-post-thumbnail","hentry","insight_category-guides","insight_tag-conversion","insight_tag-performance","insight_tag-web-development"],"acf":[],"_links":{"self":[{"href":"https:\/\/dextora.agency\/en\/wp-json\/wp\/v2\/insight\/8240","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/dextora.agency\/en\/wp-json\/wp\/v2\/insight"}],"about":[{"href":"https:\/\/dextora.agency\/en\/wp-json\/wp\/v2\/types\/insight"}],"author":[{"embeddable":true,"href":"https:\/\/dextora.agency\/en\/wp-json\/wp\/v2\/users\/5"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/dextora.agency\/en\/wp-json\/wp\/v2\/media\/8236"}],"wp:attachment":[{"href":"https:\/\/dextora.agency\/en\/wp-json\/wp\/v2\/media?parent=8240"}],"wp:term":[{"taxonomy":"insight_category","embeddable":true,"href":"https:\/\/dextora.agency\/en\/wp-json\/wp\/v2\/insight_category?post=8240"},{"taxonomy":"insight_tag","embeddable":true,"href":"https:\/\/dextora.agency\/en\/wp-json\/wp\/v2\/insight_tag?post=8240"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}