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

VoltDropCalc is one of 52 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.com
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.
Total Interest Calculator
totalinterestcalc.com
The full interest cost over a loan's life, laid out across terms and rates so you can see what a lower rate or shorter term really saves before you sign.
SIP Calculator
sipcalculatorhub.com
Systematic investment plan projections for mutual funds — expected returns by rate, tenure and step-up amount, with the compounding shown year by year.
Calorie Calculator
calorieskit.com
Daily calorie targets, BMR and a macro split for cutting, maintaining or bulking — a clear starting point for planning meals without the fad-diet noise.
BMI & BMR Calculator
bmibmrcalc.com
Body mass index and basal metabolic rate from height, weight, age and sex — where you sit on the scale and how many calories you burn at rest.
Fraction Calculator
fractionsteps.com
Add, subtract, multiply and divide fractions with every step of the working shown — for homework, recipes and measurements that refuse to be decimals.
GPA Calculator
gpacalculatorhq.com
Grade point average and cumulative CGPA from letter grades and credit hours across common scales — track standing and work out the marks you still need.
AC Tonnage Calculator
actonnagecalc.com
The air-conditioner size in tons a room actually needs from floor area, climate and insulation — so you avoid a unit that short-cycles or can't keep up.
Tank Volume Calculator
tankvolumecalc.com
Volume and fill level for cylindrical, rectangular and oval tanks in any unit — sized for water storage, fuel, aquariums and process vessels.
Pool Volume Calculator
poolvolumecalc.com
Swimming-pool water volume in gallons or litres for rectangular, round and irregular shapes — the number behind dosing chemicals, heating and refills.
Cubic Yardage Calculator
cubicyardage.com
Cubic yards of concrete, gravel, mulch, soil or sand from simple dimensions — order the right load of material instead of guessing and paying twice.
Concrete Material Calculator
concretematerialcalc.com
Concrete, cement, sand and aggregate quantities for slabs, footings and columns — plan a pour and buy bags in the right mix ratio.
Roofing Material Calculator
roofingmaterialcalc.com
Shingles, underlayment and materials estimated from roof area and pitch — budget a re-roof and cut the leftover waste before ordering.
Stair Calculator
staircalculators.net
Rise, run, stringer length and step count worked out to building-code limits — plan a safe, comfortable staircase before any timber is cut.
Construction Calculators
constructioncalchq.com
A hub of construction calculators for materials, areas, volumes and estimates in one place — the everyday jobsite math for builders and DIYers.
Solar Battery Bank Calculator
solarbatterybankcalc.com
Battery bank sizing from daily load, days of autonomy and depth of discharge — the storage math for off-grid and backup solar systems.
Backup Power Calculator
backuppowercalc.com
Generator and battery sizing from appliance wattage and the runtime you need — plan for outages without over- or under-buying capacity.
Cooking Measurement Converter
measurechef.com
Cups, grams, ounces, millilitres and spoons converted for real recipes — scale servings up or down with kitchen measures that actually line up.

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.
Internet Speed Test
checkinternetspeed.tools
Download, upload and ping measured straight in the browser — a fast read on latency and throughput when a connection feels slower than it should.
What Is My IP
checkmyipnow.com
Your public IP with the location, ISP and browser details sites can see — handy for VPN checks, remote access and network troubleshooting.
WHOIS Lookup
whoislookuppro.com
Domain registration, ownership, expiry and DNS records for any site — for buying domains, tracking renewals and researching who runs a page.

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.
Number to Words
numtotext.com
Numbers spelled out in words for cheques, invoices and contracts — handles currency and large figures so the written amount matches the digits exactly.

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