Mohamed Zakrya
Mohamed Zakrya builds calculator and tools websites, including Viral Rang and RekenmachinePro.nl. Every tool he ships shows its formula and is covered by automated tests.
Articles
Time and a Half: The Regular Rate Is Not Your Hourly Wage
Every explanation says multiply your hourly rate by 1.5. That is the wrong number the moment a bonus, a shift differential, or a second pay rate enters the week.
8 min read
Federal Holidays: the Dates, and the Rules Behind Them
Eleven federal holidays — but not always eleven days off. The holiday keeps its statutory date; only the day off moves, and sometimes it moves into the next year.
8 min read
How Many Working Days Are in a Year?
250 working days, 2,000 hours, exactly 50 five-day weeks. That tidy set of numbers is true this year and wrong next year, and the leap year is not the reason.
6 min read
Why the Quadratic Formula Loses Accuracy on One of Its Two Roots
Completing the square takes four lines and produces the formula. It also shows which of the two roots is safe to trust, and the calculator on this site was corrected to use the other route.
10 min read
Why the Minimum Payment Shrinks as Fast as the Balance
The first minimum on a 5,000 balance at 22% is 101.83, and 10.17 of it touches the debt. Hold that same figure instead of paying it and the same money clears the card 690 months sooner.
10 min read
Why a Taller Person Gets a Higher BMI for the Same Build
Three numbers in the formula were chosen rather than measured: the exponent, the constant, and the line at 25. One of them is worth nine grams. Another is worth five index units.
10 min read
How Many Decimals to Keep When Converting Units
The factor is exact to nine digits. The measurement you typed is good to one. Only one of those two limits the answer, and it is not the factor.
9 min read
Geometry Backwards: Finding the Radius from the Area
Every geometry formula is printed in the direction you need least. Running it backwards is not the same operation reversed; it is a root, and roots can refuse.
10 min read
When Cross Multiplication Gives You the Wrong Answer
Cross multiplication answers every question you put to it, including the ones it should refuse. The test is one line: if the input were zero, would the output be zero?
10 min read
Scale Factor: Why Doubling the Size Gives Four Times the Area
Twice as big means four times the paint and eight times the water. Lengths take k, areas take k², volumes take k³, and every scaling error is the wrong exponent.
9 min read
Percent Grade to Degrees: Why a 100% Grade Is 45 Degrees, Not Vertical
A 100% grade is 45 degrees. Percent grade has no ceiling; degrees stop below 90, and that mismatch is where every conversion error starts.
9 min read
How to Add Fractions With Different Denominators — and Why the Rule Works
1/2 + 1/3 done the wrong way gives 2/5 — smaller than the 1/2 you started with. A sum must beat both addends, and that check is free.
10 min read
Converting Temperature Differences: Why 10 °C of Change Is 18 °F, Not 50
A day that warms from 10 °C to 20 °C warms by 18 °F, not 50. The 32 belongs to temperatures — a difference never sees it.
9 min read
Percentage Difference vs Percentage Change: Which One Do You Want?
40 and 60 are 40% apart, 50% more, and 33.3% less. All three are correct. The denominator is the decision.
9 min read
How Long Should a Password Be?
Eight characters with every symbol you can find: 5 hours. Twelve lowercase letters and nothing else: 6 days.
10 min read
How Time Card Rounding Changes Your Overtime Pay
The same 70 minutes of rounding is worth $25.67 in one week and $38.50 in the next. Nothing changed but the total.
10 min read
What Size Solar System Do I Need to Go Off Grid?
7 panels cover a 10 kWh day with 0.08 kWh to spare. Refilling the battery on that surplus takes 125 days.
10 min read
How Long Will a Battery Run My House? The Two Tests It Has to Pass
A 100 Ah battery is 1,200 Wh, 600 Wh of it usable — and none of that says whether your fridge will start.
9 min read
What Is Power Factor? The Current Your Watts Do Not Show
Watts describe the result. Volt-amps describe the burden — and conductor heating follows the square of the difference.
9 min read
What Is a Demand Charge? Load Factor and Your Real Rate per kWh
Two businesses on one tariff can pay 22.27 cents and 14.57 cents a kilowatt-hour, decided by nothing but how evenly they drew power.
9 min read
What Size Wire Do I Need? Voltage Drop Over a Long Run
The current goes out and comes back, so a 100 ft run is 200 ft of copper — and moving to 240 V helps twice over.
9 min read
How Many Gallons Is My Pool? Average Depth and the Three-Part Floor
The mean of the shallow and deep ends is exact for one shape of floor, and most pools are not that shape.
9 min read
How Many Stairs Do I Need? Risers, Treads and the Code Edge
You do not choose the riser height. You choose how many, and the height is whatever the division hands back.
9 min read
How Much Insulation Do I Need? R-Value, Inches and Bags
The target is an R-value, the depth is inches, and the purchase is bags — and bags never come from the inches.
9 min read
How Many Deck Boards Do I Need? Rows, Gaps and the Fencepost
A six-inch board is three different widths, and the gap between boards is part of what they cover.
9 min read
How Much Carpet Do I Need? Runs, Seams and the Roll Width
A 280 sq ft room takes 352.8 sq ft of carpet, and only 14 of those extra feet are the trim allowance.
9 min read
How Many Pavers Do I Need? Pavers, Base, Bedding and Joint Sand
Four quantities come out of one measurement, and the paver count is the easy one — the base is where a patio is usually ordered short.
9 min read
How Much Roofing Do I Need? Squares, Bundles and the Pitch Multiplier
The one material on a house where the area you measure and the area you buy are different numbers, and the arithmetic that separates them.
8 min read
Sod or Seed: Which One Your Site Will Actually Let You Use
The five site conditions that settle a lawn-establishment method before cost gets a vote, and how to compare the two orders once they do.
9 min read
How to Schedule a Meeting Across Time Zones Without DST or Date-Line Mistakes
A workflow for choosing, validating, and communicating a meeting time when offsets, calendar dates, and daylight-saving transitions can differ.
10 min read
How to Claim a Trip Back: Mileage or Actual Cost, Per Diem or Receipts
A method-first guide to choosing vehicle, meal, and lodging claims that match the claimant, governing rules, and available evidence.
11 min read
How to Find the Volume of Hollow, Partial, and Composite Solids
A decomposition-first guide to pipes, frustums, domes, and partly filled tanks, with formulas and checks for avoiding geometric and unit errors.
12 min read
How to Compare Two Data Sets: Center, Spread, and Relative Difference
A practical workflow for deciding whether two sets are comparable, describing their typical values and variation, and reporting differences without overstating them.
10 min read
Putting JSON in a URL: Validate, Minify, Percent-Encode, or Base64url?
A decision guide for flattening, encoding, checking, and safely transporting JSON in a query string.
9 min read
How Long to Cook a Turkey: The USDA Times, and Why They Are a Window
Weight gives you a schedule. A thermometer gives you a finish. The gap between those two ideas is where most turkey advice goes wrong.
13 min read
Instant Yeast vs Active Dry: Four Rules, and Two Fail Their Own Reversal
Convert one way, convert back, and see whether you land where you started. Two of the four published rules do not.
14 min read
How Much Yeast Is in a Packet? Seven Grams, and Three Quarters of a Tablespoon
The teaspoon answer is everywhere. The tablespoon answer is the one people actually need, because a whole tablespoon is a third too much.
11 min read
A Stick of Butter, in Every Unit — and the Two Shapes Nobody Mentions
The stick is the one American measure that works cleanly — right up to the moment a recipe asks for a third of a cup.
12 min read
180°C Is Gas Mark 4 — and the Chart That Says So Is Not a Conversion
The gas mark scale is Fahrenheit. The Celsius numbers next to it are dial settings someone chose, which is why they nearly work and occasionally do not.
11 min read
Baking Pan Sizes: The Two Loaf Pans, the Sheet Ladder, and the One Rule That Governs Both
A pan substitution is an area problem. Get the area right and the only thing left to manage is how deep the batter sits — which is what actually decides the bake.
12 min read
How Many Grams in a Cup? Every Ingredient, One Chart
One formula, fourteen densities. Why flour is 120 g, honey is 340 g, and the ingredient — not the cup — decides the number.
14 min read
How Much Water Should You Drink a Day? Real Numbers, Not the 8-Glass Myth
A baseline from your body weight, two flat top-ups for activity and heat — and why the eight-glass rule is one specific person's answer.
13 min read
How to Calculate Body Fat Percentage: Tape-Measure Math That Works
Three tape measurements, one logarithmic formula, a neutral reference band — and why the free method holds up against a lab scan.
12 min read
Carry-On Weight Limits by Airline: What Each One Actually Publishes
The question assumes a rule that the three largest US airlines do not have. What they publish instead is stranger, and more useful to know.
12 min read
How to Connect a Portable Generator to Your House
One decision picks your method: are you powering things, or powering circuits? Everything else follows from that, including whether you need an electrician at all.
14 min read
What Size Generator Do I Need? Wattage by Scenario
Running watts plus one surge, times 1.2. The honest tally that gets it right, and the mistake that stalls a generator the moment the compressor kicks in.
13 min read
How Much Does Heating Cost? By Fuel, Per Month, With Math
The watts-times-hours formula, the $63 default month, why every 1,500 W heater costs the same to run, and where gas and heat pumps land.
13 min read
How to Calculate a Discount: Sale Prices, Stacked Deals, and Tax
The percent-off formula, the sequential math behind stacked deals, and the discount-then-tax order the register actually uses.
13 min read
How Is Sales Tax Calculated? Rates, Rules, and the Reverse Math
The combined-rate reality, the one-multiplication forward formula, and the division that pulls the tax back out of any total.
13 min read
How Does Inflation Work? The Math That Shrinks Money
One growth factor, two answers — what today's money will buy later, and how many future dollars it takes to keep up.
13 min read
How Much Will Gas Cost for My Trip? Road-Trip Fuel Math
Three numbers set the fuel bill: miles driven, the MPG you actually get, and today's price. Most bad estimates get the middle one wrong.
12 min read
How Much Should You Tip? Rates by Situation, With the Math
The customary rates by setting, the three-line formula, and the split order that keeps the tip at the rate you chose.
12 min read
How Are Loan Payments Calculated? Amortization, Explained
One level payment, front-loaded interest — the formula worked by hand, the two levers you control, and why the smaller payment is often the costlier loan.
13 min read
How to Calculate Take-Home Pay: From Gross to What You Keep
One combined deduction rate, your pay schedule, and a two-minute pay stub calibration — gross to net in two lines of math.
13 min read
What Is TDEE? Total Daily Energy Expenditure, With Real Numbers
The resting floor, the activity multiplier that scales it, and how to read the maintenance number that comes out.
13 min read
How Much Protein Do I Need a Day? Grams by Goal and Body Weight
Your weight in kilograms times a goal factor. The factor is the whole story — and the range matters more than the number.
13 min read
How Much Does It Cost to Charge an EV? Home vs Public, Per Mile
The three-line formula, the losses you pay for but never keep, and why home charging beats public by two to four times.
13 min read
How Many Solar Panels Do I Need? Sizing From Your Real Usage
Daily usage divided by what one kilowatt makes in a day, why sun hours dominate the count, and the wattage trade that saves a tight roof.
13 min read
How Much Does Electricity Cost? Reading Your Bill in kWh
The kWh formula, the rate your bill actually charges, and what a heater, an always-on device, and standby power really cost.
6 min read
How Much Flooring Do I Need? Boxes, Waste & Room Math
Floor area is the easy part. Waste tiers, box coverage, and rounding up are where the order goes wrong.
7 min read
How Many Tiles Do I Need? Sizes, Waste & Boxes
The formula, the waste allowance that actually fits your layout, and how to turn a tile count into whole boxes.
7 min read
How Much Drywall Do I Need? Sheets, Mud & Screws
The area formula with the standard opening deductions, the sheet-size trade-off, and the mud, tape and screw counts that go with it.
6 min read
How Many Rolls of Wallpaper Do I Need? Pattern Repeat Math
The wall-area takeoff, the usable yield of a roll, and why the pattern repeat decides your order.
6 min read
How Much Fencing Do I Need? Posts, Panels & Gates
One section count drives the whole bill of materials — posts, panels, gates, and the concrete nobody tallies before the store run.
7 min read
How Much Grass Seed Do I Need? Rates by Grass Type
The rate for every grass type, the half rate for overseeding, and the seeding window that decides whether any of it works.
7 min read
What Size Air Conditioner Do I Need? BTU by Room Size
Floor area gives you the base number. Ceiling height, sun, bodies and a kitchen decide whether you buy that unit or the next one up.
7 min read
How Does Compound Interest Work? The Math That Grows Money
Interest that earns interest — the formula, the frequency gap, and why steady deposits and time do most of the work.
7 min read
What Is My BMR? Basal Metabolic Rate, Explained With Numbers
The Mifflin-St Jeor equation, what each input is worth, and why BMR is the floor of your calorie needs — never the budget.
6 min read
How Much Paint Do I Need? The Complete Room-by-Room Guide
A gallon covers about 350–400 sq ft — but the real number depends on coats, surface, and sheen. Here's how to get it right, with a room-size cheat sheet and the calculator to do the math for you.
7 min read
How Much Concrete Do I Need? Slab Math, Bag Counts, and When to Call the Truck
Yards and bag counts for real projects — patios, shed slabs, and deck piers — with the ordering math nobody tells you.
6 min read
How Much Gravel Do I Need? Driveways, Paths & Drainage
The volume formula, the tons conversion, and the right depth and stone for every job.
7 min read
How Much Topsoil Do I Need? Lawns, Beds & Topdressing
The volume formula, the right depth for each job, and how topsoil differs from garden soil, compost, and fill dirt.
7 min read
How Much Mulch Do I Need? Bed-by-Bed Math in Yards and Bags
Real numbers for straight beds, curved borders, and tree rings — plus which mulch to actually buy.
7 min read
How to Pest-Proof Your Home Before Vacation
Cut off food, moisture, and entry points before you leave — so you come home to your house, not to ants, mice, or pantry moths.
7 min read
Laphing 101: Everything You Need to Know About This Tibetan Delicacy
Laphing is Tibet's spicy cold-noodle street food — slippery mung-bean jelly noodles in fiery chili sauce. Learn its origins, how it's made, and how to make it at home.
17 min read
Red Heart Emoji ❤️ Meaning: Texting, Snapchat & How to Use It
The red heart is the internet's default symbol for love — but its real meaning depends entirely on who sends it and when. Here's how to read ❤️ in texts, on Snapchat, and across every app.
6 min read
Green Heart Emoji 💚 Meaning: Texting, Snapchat & How to Use It
The green heart is the internet's friendliest, most versatile heart — it can mean nature, support, jealousy, or Irish pride. Here's how to read 💚 in texts and across every app.
6 min read
Black Heart Emoji 🖤 Meaning: Texting, Snapchat & How to Use It
The black heart is the moodiest emoji in the keyboard — it can mean dark humour, grief, edgy affection, or solidarity. One thing it almost never means: hate. Here's how to read 🖤.
6 min read
Blue Heart Emoji 💙 Meaning: Texting, Snapchat & How to Use It
The blue heart is the calm, loyal, 'I've got your back' heart — trust and friendship more than romance. Here's how to read 💙 in texts, including the friend-zone question, and across every app.
6 min read
Yellow Heart Emoji 💛 Meaning: Texting, Snapchat & How to Use It
The yellow heart is the friendship-and-sunshine heart — happy, warm, and platonic. It's also the one heart with a real Snapchat meaning. Here's how to read 💛 in texts and on Snapchat.
6 min read
Purple Heart Emoji 💜 Meaning: BTS, Texting, Snapchat & How to Use It
The purple heart means affection, admiration, and compassion — and carries two big extra meanings: BTS's 'I purple you' and the U.S. military medal. Here's how to read 💜.
6 min read
Orange Heart Emoji 🧡 Meaning: Texting, Snapchat & How to Use It
The orange heart is the warm, supportive 'middle child' between yellow friendship and red romance — care without the pressure. Here's how to read 🧡 in texts and across every app.
6 min read
White Heart Emoji 🤍 Meaning: Texting, Snapchat & How to Use It
The white heart is the soft, pure, minimalist heart — gentle affection, peace, and sympathy. Here's how to read 🤍 in texts and across every app.
5 min read
Brown Heart Emoji 🤎 Meaning: Texting, Snapchat & How to Use It
The brown heart is the warm, earthy, comforting heart — cosy affection, and a symbol of solidarity and pride. Here's how to read 🤎 in texts and across every app.
5 min read
Broken Heart Emoji 💔 Meaning: Texting, How to Reply & How to Use It
The broken heart is the internet's universal 'it hurts' stamp — real heartbreak, sympathy, or dramatic irony. Here's how to read 💔, how to reply when someone sends it, and how it works across apps.
5 min read
Two Hearts Emoji 💕 Meaning: Texting, Snapchat & How to Use It
The two hearts emoji is the warm, 'love is in the air' heart — affection, cuteness, and romance. It's also Snapchat's top friendship badge. Here's how to read 💕 everywhere.
5 min read
Growing Heart Emoji 💗 Meaning: Texting, Snapchat & How to Use It
The growing heart is the 'my heart is swelling' emoji — affection that's getting bigger, warmer, stronger. Here's how to read 💗 in texts and across every app.
5 min read
Sparkling Heart Emoji 💖 Meaning: Texting, Snapchat & How to Use It
The sparkling heart is the bubbly, glittery, excited-love heart — affection with extra shine. Here's how to read 💖 in texts and across every app.
5 min read
Pink Heart Emoji 🩷 Meaning: Texting, Snapchat & How to Use It
The pink heart is the soft, sweet, tender heart — gentle affection without the intensity of red. Here's how to read 🩷 in texts, why it's not the Snapchat badge, and how it works everywhere.
5 min read
Heart Emoji Meanings: What Every Heart Color & Symbol Means
Dozens of heart emoji, each with its own meaning. Here's the complete guide — every colour and every type explained, with a link to a deep dive on each one.
8 min read