Some questions come up every week: what does this cron line actually do, what date is this timestamp, how many requests per second is 600 a minute, how much downtime does 99.9% allow. The answers are simple, but a slip in the conversion causes real bugs.
These tools answer them instantly and show the working, so you can paste the reasoning into a pull request or an incident note.
Time and scheduling
Read cron schedules in plain English and convert epoch timestamps.
- Cron Expression ExplainerPaste a cron schedule to read it in plain English, see the next run times, and check how often it will fire before it goes to production.
- Unix Timestamp ConverterConvert a Unix timestamp to a human-readable UTC date, or the reverse. Instant, with no rounding surprises.
- Timezone Meeting PlannerCompare working hours across several timezones at once and find the windows that actually overlap.
Frontend
Colours, rem units and aspect ratios for responsive layouts.
- Color Code ConverterConvert a HEX color to its RGB and HSL equivalents, instantly, with the exact values CSS expects.
- PX to REM ConverterConvert pixels to rem and rem back to pixels for any root font size, with the CSS value ready to copy.
- Aspect Ratio CalculatorFind the aspect ratio of any width and height, and work out the matching height when you resize to a new width.
Data and numbers
Number bases, storage units and transfer times.
- Number Base ConverterConvert a number between binary, octal, decimal, and hexadecimal, instantly, in either direction.
- Data Storage ConverterConvert between bytes, KB, MB, GB, TB, and PB, using the binary (1024-based) convention operating systems actually use.
- Download Time CalculatorEstimate how long a file will take to download or upload at a given connection speed, allowing for real-world overhead.
Operations and security
Rate limits, uptime budgets, storage and egress costs, and password strength.
- API Rate Limit ConverterConvert between requests per second, minute, and day, and get a safe sustained rate with headroom built in, not just the raw math.
- Uptime and SLA Downtime CalculatorTurn an uptime percentage like 99.9% into the downtime it allows per year, month, week and day.
- Cloud Storage Cost Calculator: Amazon S3 vs Cloudflare R2Estimate your monthly object-storage bill on Amazon S3 and Cloudflare R2 from storage, downloads and requests, and see how much egress fees add.
- Password Entropy CalculatorMeasure the strength of a randomly generated password in bits of entropy, and see how long it would take to guess at different attack speeds.
- IP Subnet Calculator (IPv4 CIDR)Enter an IPv4 address and CIDR prefix to get the network and broadcast addresses, usable host range, subnet mask, wildcard mask and host count.
- chmod Calculator: Linux File PermissionsConvert Linux file permissions between numeric (755) and symbolic (rwxr-xr-x) form, see who can do what, and get the chmod command.
Questions people ask
Do these tools send my data anywhere?
No. Every calculation runs in your browser. Nothing you type is sent to our servers.
Can I link a teammate to a specific result?
Yes. Use "Copy link to these numbers" on any tool; the link opens the tool with your inputs filled in.
Can I embed a calculator in our docs?
Yes. Each calculator has an "Embed on your site" button with a ready-made code snippet. Please keep the credit link.