Calculators built for people who ship
DevCalc collects the small, exact calculations that engineers and designers reach for every day and makes them instant, private, and free. There are no logins, no upsell walls inside the tools, and no servers in the loop — every result is computed in your browser with JavaScript, so your IP plans, image dimensions, and brand colors never leave your device. Bookmark it as your go-to developer calculators tab.
Subnet calculator (IPv4 / CIDR)
The subnet calculator takes an IPv4 address and a CIDR prefix or dotted-decimal mask and returns the full picture: network address, broadcast address, first and last usable host, wildcard mask, total and usable host counts, address class, and type (private, public, loopback, CGNAT). A live slider lets you watch a /24 grow into a /23 or shrink to a /26, and it handles the /31 and /32 edge cases per RFC 3021. Perfect for VLAN planning, cloud VPC sizing, firewall ACLs, and CCNA practice.
Aspect ratio calculator
The aspect ratio calculator solves the proportion W₁/H₁ = W₂/H₂. Enter your original dimensions and a single new width or height, and it computes the matching dimension so nothing stretches; it also reduces any size to its simplest ratio (like 16:9) using the greatest common divisor. Presets cover 16:9, 4:3, 1:1, 3:2, 21:9 and 9:16, with a live proportional preview — handy for responsive images, video exports, social crops, and avoiding layout shift.
Color contrast checker
The color contrast checker implements the WCAG 2.1 relative-luminance formula and reports the exact contrast ratio (1:1 to 21:1) plus pass/fail badges for AA and AAA across normal text, large text, and the 3:1 UI-component threshold. A live preview shows your text on your background in real time, with a color picker, hex input, swap button, and quick swatches so you can dial in an accessible palette in seconds.
Why client-side calculators are better
- Privacy: infrastructure addresses, design files, and brand colors stay on your machine.
- Speed: zero round-trips means answers update as you type.
- Reliability: the math keeps working even if your connection drops.
- Transparency: the formulas are documented on each page, so you can verify every number.
DevCalc is part of the hjLabs.in family of free tools, alongside the JSON & data formatter, the favicon & OG image generator, the image-to-C++ converter for Arduino, the AI image enhancer, and the DPDPA privacy policy generator. More calculators are on the way.