Free Math & Calculators Tools & Calculators
Browse 710+ free interactive math & calculators calculators, estimators, and utilities. 100% free, private, and runs directly in your browser without signup.
Significant Figures Counter & Rounding Calculator
Free significant figures counter: count sig figs in any number, see which digits are significant, which rule applies, and round to N significant figures — 100% client-side.
Simplify Radicals Calculator — Simplify √, ∛ & nth Roots Step by Step
Free simplify radicals calculator: reduce √72 to 6√2, ∛54 to 3∛2 and any ⁿ√x to simplest a·ⁿ√b form with prime-factorization steps. Add and subtract like radicals too.
Small Business Tax Calculator – LLC, Freelancer & Sales Tax
Small business tax calculator, wa tax calculator, how to determine sales tax, ma sales tax calculator, georgia state tax calculator, how much would i pay in taxes calculator, how much taxes will i owe calculator, how to find tax on an item, how to calculate sales tax percentage from total, agi tax calculator, tax calculator llc, self employed tax return calculator, how to figure tax on purchase, american sales tax calculator, tax rate calculator california, tn income tax calculator, tax calculator for freelancers, llc tax calculator with deductions, how to find tax on a calculator, how to calculate sales tax on a calculator, how to figure out tax on a calculator, convert sales tax, formula for figuring sales tax, sales tax and tip calculator, sell tax calculator, sales tax calculator usa.
Snowshoe Size Calculator — Find Your Perfect Snowshoe Size & Fit
Free snowshoe size calculator: enter body + gear weight, snow conditions and terrain to get the right snowshoe size. Real manufacturer charts (MSR, Tubbs, Atlas, Yukon Charlie's, TSL), binding fit guide, kids & women's sizing.
Soap Making Cost Calculator — COGS, Pricing & Break-Even Suite
Free soap making cost calculator: build your true cost per bar from supplier prices (oils, lye, fragrance, packaging), add labor & overhead, price by margin, markup or wholesale 2x/4x, check Etsy, Shopee and Tokopedia fees, compare making vs buying, and find break-even. 18 currencies. 100% client-side, no signup.
Sock Size Calculator — Cast-On, Heel & Foot Size Chart for Knitters
Free sock size calculator for knitters: cast-on stitches from foot circumference × gauge with negative ease, heel flap + row-by-row heel turn schedule, gusset pickup math, toe-up mode, foot length chart by shoe size (US/UK/EU), cuff & leg planner and yarn estimate. 100% client-side.
Solar Panel Calculator — Size, Cost, Savings Payback (Global)
Free solar panel calculator: size your system from your electric bill (kWh, peak sun hours), estimate 25-year savings with degradation and tariff inflation, payback year, LCOE, battery backup, RV/campervan off-grid, tilt angle, and CO2 offset. Works worldwide, 20 currencies. 100% client-side.
Solenoid Inductance Calculator — Wheeler, Nagaoka & Wire Estimator
Free solenoid inductance calculator: Wheeler formula, long-solenoid SI formula, Nagaoka end-correction, wire length, copper AWG DC resistance, LC resonant frequency, and a turns-for-target-L design mode. 100% client-side.
Sous Vide Time Temperature Calculator — Baldwin-Based Pasteurization Times
Free sous vide time and temperature calculator based on Douglas Baldwin's pasteurization tables. Steak, chicken, pork, salmon, brisket, eggs — thickness, frozen & doneness aware. 100% client-side, no signup.
Speed of Light Calculator — c = 299,792,458 m/s
Free speed of light calculator: c = 299,792,458 m/s exact. Convert m/s, km/s, km/h, mph, ft/s, mi/s; time-of-flight Earth–Moon & Sun; c = λν wavelength–frequency solver; light-year distances; refractive slowdown v = c/n.
Speed of Sound Calculator — Air, Altitude, Humidity, Mach Number & Echo Distance
Free speed of sound calculator: c = 20.05√T in air with altitude (ISA) and humidity correction, Mach number, sound speed in water, steel and helium, echo distance d = c·t/2, and a speed unit converter. 100% in-browser, no sign-up.
Speeds & Feeds Suite — RPM/SFM, Feed Rate, Chip Load, Tapping, MRR + Power Calculator
Free speeds and feeds calculator suite: RPM/SFM solver, milling & lathe feed rate calculator, material speed database (HSS/carbide/cobalt), chip load advisor, tapping speeds & feeds, MRR + spindle power estimator, and printable reference charts. Imperial + metric.
Sphere Density Calculator — Bulk Density & Packing Density (SC, BCC, FCC, HCP)
Free sphere density calculator with two modes: (1) bulk density of a solid sphere from mass and radius, ρ = m / V with V = 4/3·π·r³; (2) sphere packing density — SC, BCC, FCC, HCP, random close/loose packing fractions, ball count in a container and packed-bed bulk density. 100% in-browser.
Spousal Support Calculator (SSAG) — Alimony Estimator + Buyout & Property Split
Free spousal support calculator: Canadian SSAG without-child and with-child (INDI) formulas, Rule of 65 duration, lump-sum alimony buyout present value, US state estimators (MA, TX, CT), Ontario property equalization and community-property split. 100% private, works offline.
Spring Rate Converter — N/mm, lb/in, kg/mm + Hooke, Series/Parallel & Wheel Rate Calculator
Free spring rate converter: convert N/mm, N/m, kN/m, lb/in, lb/ft, kg/mm, kgf/mm both ways. Includes Hooke's law F=k·x solver, series & parallel spring calculator, and wheel rate from motion ratio. 100% client-side.
Square Diagonal Calculator — Side ⇄ Diagonal + Area from Diagonal
Free square diagonal calculator: side to diagonal (d = s√2), diagonal to side (s = d/√2), area from diagonal (A = d²/2), live diagram, show-your-work steps and worked examples.
Square Inches Calculator — Area in in² (Rectangle, Circle, Triangle, Trapezoid)
Free square inches calculator: area in square inches for rectangle (L×W), circle (πr²), triangle (½bh), trapezoid ((a+b)/2×h), reverse side-from-area solver, and full conversion to sq ft, sq cm, sq yd, sq m, sq mm, acres.
Squat Max Calculator — Estimate Your 1RM (Epley, Brzycki, Lombardi)
Free squat max calculator: estimate your squat 1RM from weight × reps with Epley, Brzycki and Lombardi formulas. Training % table, rep-max chart, plate loader, bodyweight ratio, kg/lb.
Standard Error of the Mean Calculator (SEM) + Confidence Interval
Free standard error of the mean calculator: enter sample SD and n to get SEM = s/√n, plus a 90/95/99% confidence interval for the mean (z or t), t-critical table, and worked examples.
Standard Equation of a Circle Calculator — (x-h)²+(y-k)²=r²
Free standard circle equation calculator: find (x-h)^2+(y-k)^2=r^2 from center+radius, three points, or general form x^2+y^2+Dx+Ey+F=0 (completing the square). Shows center, radius, general form and graph.
Standard Normal Curve Calculator & Z-Score Percentile Tool
Interactive standard normal curve calculator, standardized value z score, normal distribution curve z score, and percentile rank converter.
Standard Normal Distribution Calculator – Z Score & Probability
Standard normal distribution calculator, standard normal distribution probability calculator, z score meaning, z statistic formula, what does z score represent, define z score, normal distribution z score, how to get p value from z score, z to p value, calculator z test.
Stiffness Matrix Calculator | nrtechstudio
Free stiffness matrix calculator: axial bar (2x2), Euler-Bernoulli beam (4x4), 2D truss with angle transformation, and a 2-element assembly solver wit
Stress Concentration Factor (Kt) Calculator — Hole, Fillet, Notch + Kf
Free stress concentration factor calculator: Kt for a hole in a plate (Heywood), shoulder fillets in tension & bending (Peterson chart curve-fits), notches (Inglis), plus fatigue Kf via Neuber notch sensitivity q. 100% in-browser, no sign-up.
String Length Calculator
Advanced character length calculator, UTF-8 byte size counter, and string memory analyzer for developers.
Stripe Fee & Payout Calculator
Free online Stripe fee calculator to compute credit card processing deductions (2.9% + $0.30), international card fees, and exact gross invoices.
Stroke Volume Calculator (SV = EDV − ESV, SV = CO/HR, SVI) — nrtechstudio
General stroke volume calculator: SV = EDV − ESV, SV = CO/HR, and stroke volume index
Sub Business Days
Subtract working business days from a date.
IPv4 Subnet Mask & CIDR Calculator
Free online IPv4 subnet calculator to determine network address, broadcast IP, usable host range, CIDR prefix (/8 to /32), and wildcard mask.
Sun Angle Calculator — Solar Altitude & Azimuth, Sunrise/Sunset
Calculate accurate sun angle (solar altitude & azimuth) from latitude, longitude, date, and timezone. Includes sunrise, sunset, solar noon, declination, equation of time, day length, shadow length estimate, and hourly table.
Surfboard Volume Calculator — Liters by Dimensions, Ideal Volume Finder & Quiver Compare
Free surfboard volume calculator: estimate liters from dimensions with per-board-type coefficients calibrated against real published boards, find your ideal volume with 3 methods side-by-side, reverse-solve dims from liters, compare your quiver, and size boards for kids. 100% private — runs in your browser.
CCTV Storage Calculator — NVR/DVR Storage Planner Camera Recording Time
Free CCTV storage calculator & NVR/DVR storage planner: plan multi-camera storage by resolution, fps, codec (H.264/H.265), motion detection % and retention days. Vendor bitrate presets (Dahua, Hikvision, Axis, Bosch), recording-time inverse, GoPro/dashcam SD-card recording time, codec comparison. 100% client-side.
Swarm Trap Size Calculator — Ideal Volume, Entrance & Lure Guide
Free swarm trap size calculator: check your trap volume against Seeley's 40-liter ideal, size the entrance hole (~15 cm²), dose lemongrass oil lure, score your trap placement, and follow a monitoring checklist. 100% client-side.
Swim Pace Lab — CSS Calculator, Pace Converter, Training Zones & Race Predictor
Free swim pace lab: convert pace per 100m / 100 yards / 50m, calculate Critical Swim Speed (CSS) from 400+200 or 1500+400 time trials, get 5 CSS training zones, predict triathlon swim-leg times (sprint, Olympic, 70.3, Ironman), adjust pool pace for open water, and convert stroke paces. 100% client-side.
Takeoff & Landing Distance Calculator — Koch Chart, Runway Verdict (Free)
Free takeoff and landing performance suite: takeoff distance estimator with Koch-chart corrections (density altitude, weight, wind, grass, slope), landing distance calculator, interactive Koch chart, runway required-vs-available verdict, accelerate-stop estimator. C172, C152, PA-28, SR22 presets. 100% client-side.
Tangent & Math Solver Calculator
The ultimate Tangent Calculator, Online Algebra Calculator, and Scientific Math Solver with step-by-step trigonometry, fractions, and complex numbers. 100% SEMrush keyword optimization.
Tax Bracket Calculator (Federal & State)
Interactive US federal and state tax bracket calculator with marginal vs effective rate breakdown, California state tax calculator, and Texas sales tax.
Tax Calculator
Calculate income tax, paycheck deductions, sales tax, and GST/VAT.
Tax Return & Sales Tax Calculator
Universal Federal & State Tax Return Refund Calculator, Multi-State Sales Tax Calculator & Pre-Tax Purchase Math.
Telescope & Eyepiece Calculator — Magnification, True FOV, Exit Pupil, Ladder Planner
Free 5-in-1 telescope eyepiece calculator: magnification, true field of view, exit pupil, Dawes limit and limiting magnitude, plus an eyepiece ladder planner, will-it-fit target checker, FOV visual and a reverse eyepiece solver. 100% client-side, no signup.
Telescope Field of View Calculator — True FOV, Exit Pupil & Dawes Limit
Free telescope field of view calculator: true field of view, magnification, exit pupil, Dawes limit, limiting magnitude and what fits in your eyepiece. 100% client-side, no data leaves your browser.
Tempo Detector & BPM Tap Calculator
Free online tempo detector and BPM tap calculator. Tap to measure beats per minute, detect song tempo, and calculate BPM with visual metronome feedback.
Tempo Tapper & BPM Calculator
Interactive tempo tapper, BPM counter, music tempo finder, metronome, delay rhythm calculator, and Hz to seconds audio tool.
Test Grade Calculator - Score to Percentage & Letter Grade
Free test grade calculator: turn correct answers into a percentage and letter grade (US standard, plus-minus, or custom scale). See points to the next grade, a what-if table, and multi-test weighted average.
Text Size Calculator & Byte Size Analyzer
Interactive text size calculator and calculate byte size tool across UTF-8, UTF-16, ASCII, and SMS encoding payloads.
Thermal Expansion Calculator - Linear, Area & Volume | nrtechstudio
Free thermal expansion calculator: linear ΔL = α·L₀·ΔT, area ΔA = 2α·A₀·ΔT, volume ΔV = 3α·V₀·ΔT. 4-way linear solver, material α table (aluminium, co
Three Phase Power Calculator — P, S, Q, PF Correction & Line/Phase
Free three-phase power calculator: real power P=√3·V·I·PF, apparent S, reactive Q, current solver, wye/delta line↔phase conversion, power factor correction capacitor sizing, and single-phase comparison. 100% client-side.
Thrust-to-Weight Ratio Calculator — T/W = F/(m·g)
Free thrust-to-weight ratio calculator: T/W = F/(m·g) with thrust in N, kN, lbf and mass in kg, lb, tonnes. Real-vehicle presets (F-16, Boeing 747, Saturn V, Starship, Space Shuttle), hover and liftoff interpretation, plus reverse solvers for thrust needed and max weight. 100% client-side.
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How to Use the Tools Directory
Every tool is a single interactive page: enter your inputs, get instant results, no account needed. Use the search box (shortcut: press /) to jump straight to a tool, or browse categories when you are exploring. Each card links to the tool's permanent URL, which you can bookmark or share.
Because all computation happens in your browser, the tools are fast, private, and free forever. If a result looks wrong, use the one-click report control on the tool page so it can be fixed.
Tool Categories at a Glance
| Category | What you will find | Example tasks |
|---|---|---|
| Developer | Encoders, formatters, regex, network tools | Format JSON, test regex, subnet a network |
| Finance | Tax, loans, salary, investing | Estimate tax brackets, amortize a loan |
| Home improvement | Estimators, measurements, materials | Size a wire, estimate paint or flooring |
| Health & fitness | Body metrics, nutrition, workouts | Track BMI, plan calories, score fitness tests |
| Math & science | Converters, geometry, statistics | Convert units, solve triangles |
| Text | Counters, sorters, generators | Count words, alphabetize a list |
| Color | Pickers, converters, checkers | Convert HEX to RGB, check contrast |
| Everyday life | Cooking, travel, automotive, pets | Convert recipes, plan fuel costs |
Popular Tasks and Where to Start
| I want to... | Start with | Why |
|---|---|---|
| Convert between number bases | Binary Converter | Step-by-step base conversion with charts |
| Validate and format data | JSON Formatter | Pretty-print and check JSON instantly |
| Count words for an essay | Word Counter | Words, characters, reading time |
| Check password strength | Password Strength Meter | Entropy-based strength scoring |
| Grade text readability | Readability Score | Flesch-Kincaid and grade levels |
| Audit color contrast | Accessibility Checker | WCAG contrast ratios in one click |
Tools Directory FAQ
What is the NRTechStudio tools directory?
It is a free catalog of more than 2,700 interactive web tools: calculators, converters, generators, and checkers for developers, finance, home improvement, health, education, and everyday tasks.
Are all the tools really free?
Yes. Every tool in the directory is free to use with no sign-up, no trial, and no paywall. They run entirely in your browser.
Do I need to create an account?
No. There are no accounts, logins, or subscriptions. Open a tool and use it immediately.
Is my data private when I use these tools?
Yes. The tools are 100% client-side: your inputs are processed by JavaScript in your own browser and never sent to a server.
How do I find the right tool?
Use the search box at the top of the directory (press / to focus it), or browse by category. Every tool card shows a short description of what it computes.
Do the tools work on mobile?
Yes. The directory and the tools use responsive layouts that adapt to phones, tablets, and desktops.
How many tools are there?
The directory holds more than 2,700 tools and grows regularly as new calculators and converters are published.
Can I request a new tool?
Yes. Each tool page has a report/feedback control you can use to request features or new tools; requests help prioritize what gets built next.
Are the tools accurate?
Calculators use published formulas and reference data (tax tables, NEC ampacity, standard conversions). Each tool page documents its method, and issues can be reported in one click for a fix.
Do tools work offline?
Once a tool page has loaded, most tools keep working without a connection because the logic is client-side JavaScript. The directory search needs the page loaded first.
What categories are covered?
Developer utilities, finance and tax, home improvement, health and fitness, math and science, text tools, color tools, networking, education, and everyday life calculators, among others.
Can I bookmark or share a tool?
Yes. Every tool has its own permanent URL under nrtechstudio.com/tools/, which you can bookmark or share directly.
Is there an API for these tools?
The tools are interactive web pages, not API endpoints. The underlying math is plain JavaScript you can inspect in the page source.
Why do some tools show ratings?
Ratings aggregate user feedback to surface the most trusted tools and flag pages that need fixes or better explanations.
How often are new tools added?
New tools are published on a continuous pipeline, prioritized by measured search demand and by user requests from the feedback controls.
Who builds these tools?
NRTechStudio, an independent tools studio focused on free, private, client-side utilities that respect user privacy.