Frequently Asked Questions
How accurate is Clockzilla?
Clockzilla synchronizes with NTP-referenced time servers and achieves accuracy typically within 100-500 milliseconds, depending on your network latency. The accuracy of each sync is displayed in the interface.
Why does my computer clock show a different time?
Computer clocks use internal oscillators that drift over time. While your OS periodically syncs via NTP, the clock can be off by seconds or more between syncs. Clockzilla measures this exact difference for you.
How does the sync work?
Clockzilla sends requests to multiple time servers, measures the round-trip network latency, and calculates the difference between server time and your local clock. It uses statistical methods to filter outliers and weight results by accuracy.
What time sources does Clockzilla use?
We use a backend proxy that fetches from 2 sources: Tier 1 is TimeAPI.io and Tier 2 is Cloudflare. The backend caches results for 3 seconds so external APIs are only called once per 3 seconds regardless of traffic. Your browser then measures round-trip latency to our server and computes your clock offset with statistical filtering.
Does Clockzilla work offline?
Clockzilla requires an internet connection to synchronize with time servers. Without connectivity, it falls back to displaying your local system time.
How often does it re-sync?
Clockzilla automatically re-synchronizes every 4 minutes. You can also trigger a manual re-sync by clicking the sync status badge in the header.
What do the accuracy ratings mean?
Excellent (under 50ms offset), Good (under 500ms), Fair (under 2 seconds), and Poor (over 2 seconds). Most modern computers connected to the internet will show Excellent or Good.
Is Clockzilla free?
Yes, Clockzilla is completely free to use. No accounts, no subscriptions, no hidden fees. The site is supported by non-intrusive ads.
Does Clockzilla support timezone conversion?
Yes. Clockzilla includes a timezone converter, a world-clock dashboard, per-city time pages for 150,000+ locations, and dedicated time-difference pages for popular city pairs.