Which calculator for which situation
- Passwords and security. Password generator creates a genuinely random password; password strength estimates entropy in bits and time to crack.
- Screens and images. Aspect ratio converts between resolutions while preserving proportions; PPI computes pixel density from the diagonal; hex to RGB converts between colour notations.
- Accessibility. Colour contrast measures the ratio between text and background and reports whether it passes WCAG AA and AAA.
- Network and infrastructure. Subnet computes range, mask and host count in CIDR; download time converts size and bandwidth into duration; uptime and SLA translates percentages into allowed minutes of downtime.
- Numbers. Base converter between binary, octal, decimal and hexadecimal.
Three numbers almost everyone misreads
Uptime. A 99.9% SLA sounds near perfect, but it permits 8 hours and 46 minutes of downtime a year. Each additional nine divides that by ten: 99.99% is 53 minutes annually and 99.999% is a little over 5 minutes. It is a logarithmic scale disguised as a percentage.
Megabyte versus megabit. Internet bandwidth is sold in megabits per second (Mbps) while files are measured in megabytes (MB). Since a byte is 8 bits, a 100 Mbps connection downloads, at best, about 12.5 MB per second. It is the origin of the feeling that broadband "never delivers what was sold".
MB versus MiB. Drive manufacturers use MB as 1,000,000 bytes; operating systems often display MiB (1,048,576 bytes) and label it MB. That is why a 1 TB drive shows up as roughly 931 GB — nothing vanished, the ruler changed.
Contrast is a rule, not an opinion
WCAG sets objective thresholds: 4.5:1 for normal text and 3:1 for large text and UI components, at level AA. The value is not arbitrary — it compensates for the effective contrast loss of someone with 20/40 acuity, common from around age 60 and not classed as a disability. Which is why contrast is not a niche concern: it affects anyone with a phone in sunlight or a dimmed screen.
Frequently asked questions
Is the generated password safe? It is created in your browser using the browser's own cryptographic generator and is never transmitted. Even so, the safest practice is to use your password manager's generator, which also stores it securely.
Why does my download never reach the advertised speed? Three reasons stack: the megabit-to-megabyte conversion, protocol overhead (on the order of 5% to 10%), and the origin server's own limit, which is rarely the bottleneck on your side.
Are PPI and DPI the same? In practice they are used interchangeably, but PPI describes pixels on a screen and DPI describes ink dots in print. The confusion is harmless until you prepare a file for a printer.
How do I choose a subnet mask? By the number of hosts required, remembering that two addresses in each range are reserved (network and broadcast). A /24 holds 254 usable hosts, not 256.