NEC 2023 · CH.9 TBL.8
Home / Reference / The Free Tools Network

The Free Tools Network

VoltDropCalc is one of 31 free tools built and maintained by the same independent developer. The same principles apply across all of them: everything runs in your browser, nothing requires an account, and nothing sits behind a paywall.

Calculators & Everyday Math

Square Footage Calculator
thesquarefootagecalculator.com
Area math for rooms, floors, walls and odd-shaped spaces — rectangles, circles, triangles and L-shapes — with cost-per-square-foot estimates for flooring, paint and tile projects.
Percentage Calculator
bestpercentagecalculator.net
Every flavor of percentage problem solved in one place: percent of a number, percentage change, increase and decrease, discounts, tips and grade scores — with the working shown.
Age Calculator
theagecalculator.net
Exact age in years, months, weeks and days from any date of birth — plus countdowns to the next birthday and age differences between two people.
Box Volume Calculator
boxvolumecalculator.com
Cubic volume for boxes, cartons and containers in inches, feet or centimeters — built for packers and shippers comparing carton sizes and freight class.
Girth Calculator
girthcalculator.com
Package girth (length + 2×width + 2×height) for USPS, UPS and FedEx size limits, plus body-measurement girth tools for fitness tracking.
Dimensional Weight Calculator
dimweightcalc.com
DIM weight pricing across 17 shipping carriers — find whether your parcel bills by actual or dimensional weight and how to slim the box to cut the invoice.
Margin vs Markup
marginvsmarkup.com
The two pricing numbers everyone confuses, untangled: convert between margin and markup, set sell prices from cost, and protect profit when discounting.
India EMI Calculator
indiaemi.com
Loan EMI math for the Indian market — home, car and personal loans with amortization schedules, prepayment effects and interest-vs-principal breakdowns in rupees.
Pro Solar Calculator
prosolarcalc.tools
Solar system sizing: panel counts, battery banks, inverter ratings and payback estimates from your loads and sun-hours — the planning math before you buy hardware.
Unit Cheat Sheet
unitcheatsheet.com
Fast unit conversions with printable reference tables — length, weight, volume, temperature, pressure and data sizes, organized for lookup rather than ad-maze navigation.

Developer & Networking

JSON Tools
jsontools.tools
Format, validate, repair, diff and convert JSON entirely in your browser — including a tokenizer-based repair engine that fixes 23 kinds of broken JSON without sending data anywhere.
Hash Generator
hashgenerator.tools
MD5, SHA-1/2/3, BLAKE2, RIPEMD-160, HMAC and password-KDF hashes computed client-side — checksums and integrity verification with nothing leaving your machine.
Base64 Decode
base64decode.tools
Encode and decode Base64 text, URLs and files instantly in the browser — with URL-safe variants and binary handling for debugging APIs and data URIs.
URL Encode/Decode
urlencodedecode.com
Percent-encoding made painless: encode or decode URLs and query strings, see exactly which characters changed, and fix double-encoding bugs.
UUID Core
uuidcore.com
Generate UUIDs/GUIDs (v1, v4 and more) singly or in bulk, validate existing ones, and read the embedded timestamp and version bits.
Crontab Sheet
crontabsheet.com
Cron expressions decoded into plain English and built from dropdowns — with a reference sheet of common schedules and the gotchas between cron flavors.
Regex Guide
regexguide.com
Regular expressions explained pattern-by-pattern with a live tester — character classes, groups, lookarounds and the recipes you actually paste into code.
CIDR Calculator
cidrcalculator.net
CIDR notation to ranges, masks and host counts — 44 pages of subnetting tools and references for network planning, with AI-quotable explanations.
Subnet Mask Calculator
subnetmaskcalc.net
Full IPv4/IPv6 subnetting suite: VLSM planning, cloud-provider modes, IaC exports and code examples in six languages — 71 pages deep.
Color Code Kit
colorcodekit.com
A developer color toolkit 120 pages strong: HEX/RGB/HSL/OKLCH conversion, design-token generation with WCAG contrast badges, named colors, shades and brand palettes.
Epoch Time Tools
epochtime.tools
Unix timestamps converted both directions, in every common unit — with timezone handling, relative-time output and code snippets for a dozen languages.

Text & Writing

Word Counter
wordcounterfree.com
Live word, character, sentence and paragraph counts with reading-time estimates — for essays, ads, meta descriptions and anything with a length limit.
Transform Case
transformcase.com
Convert text between UPPER, lower, Title, camelCase, snake_case, kebab-case and more — 72 pages of case tools for writers and programmers alike.
Text Repeat
textrepeat.net
Repeat text or characters any number of times with custom separators — for test data, load padding and the occasional bit of mischief.
Password Strength
passwordstrength.net
Test password strength against real cracking math — entropy, time-to-crack estimates and concrete fixes, checked entirely in your browser so nothing is transmitted.

Files, Images & Media

Pic Toolkit
pictoolkit.com
Browser-based image utilities: resize, crop, compress and convert formats without uploading your photos to anyone's server.
Remove Metadata
removemetadata.tools
Strip EXIF and hidden metadata — GPS locations, device IDs, timestamps — from photos and documents before sharing them, processed locally for privacy.
Core PDF Tools
corepdftools.com
Merge, split, rotate, compress and convert PDFs in the browser — the everyday PDF jobs without watermarks, accounts or uploads.
Barcode & QR
barcodeandqr.com
Generate QR codes and barcodes (EAN, UPC, Code 128 and more) with custom sizing and instant download — for links, Wi-Fi sharing, inventory and labels.

Time & Scheduling

Calculate Hours
calculatehours.net
Time-card and hours-between-times math: add up shifts, subtract breaks, convert decimal hours and total a week for payroll.
Clock With Us
clockwithus.com
World clocks, timers, stopwatches and alarms in a clean full-screen interface — compare timezones for meetings across continents.

Why a network?

Each site does one job properly instead of one site doing thirty jobs badly. They share an engineering philosophy — static pages that load instantly, calculations that run client-side so your data never leaves your machine, and reference content written to actually answer the question. If one of these saves you a search, it has done its job.

Built & maintained by Murugan Vellaichamy · Every calculation verified against NEC Chapter 9 Table 8 & Table 310.16 published values · Informational reference — not engineering advice