Guides and how-tos from the Calculator Hub team — every article pairs with one of our free calculators.
Calculator Hub Blog
Short, practical guides for the numbers that come up in real life: mortgage payments and loan EMIs, concrete and tile estimates, cooling loads and solar sizing, and everyday percentage math. Each article ends with a link to the calculator that does the heavy lifting for you.
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The Four Arithmetic Operations: A Practical Field Guide
Addition, subtraction, multiplication and division in everyday life: when order matters, sign rules for negatives, why 0.1 + 0.2 looks wrong, and how to chain sums.
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Currency Conversion: How Exchange Rates Really Work
How exchange rates work, why cross rates go through the US dollar, why your bank's rate differs from the mid-market rate, and how to convert any currency pair by hand.
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Two Calendars, One Date: How Hijri–Gregorian Conversion Works
Why the Islamic calendar drifts 11 days earlier each Gregorian year, how the Umm al-Qura calendar works, why day 30 is sometimes rejected, and what it means for Ramadan and the Eids.
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Water Pressure Pumps: Sizing Head, Flow and Power the Right Way
What total dynamic head is, the Hazen-Williams friction formula, why pipe diameter beats pump power, and how to size a domestic pressure pump without overbuying.
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Pulley Belts: How to Calculate the Right Belt Length
The belt length formula for two pulleys, worked examples with equal and unequal diameters, tensioning slack, and how to check pulley speed ratios before you buy.
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Gear Ratios Explained: Trading Torque for Speed
What a gear ratio really means, how output speed and torque are calculated, why efficiency matters, and how to pick gears for a real application.
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Bolt Torque Explained: How Tight Is Tight Enough?
Why torque specs exist, how tightening torque relates to bolt preload, the effect of lubrication, and the grades and sizes behind typical torque values.
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How Much Paint Do You Need? A Room-by-Room Guide
Calculate paint quantity the way decorators do: wall and ceiling areas, doors and windows, coats, real-world coverage per litre, and a cost estimate.
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Heat Pump Sizing: COP, Heating Load and Running Costs
How to size a heat pump from floor area and insulation, what COP really means, and how to compare running costs against gas and electric heating.
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Stair Design Basics: Rise, Run and the Rules That Keep Stairs Safe
Design a staircase that feels right: the 2R+T comfort rule, building-code limits on risers and treads, headroom, stringer length and angle.
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Cutting Speed and Feed Rate: Where Every Machining Job Starts
The difference between cutting speed, spindle RPM and feed rate, the formulas that connect them, and sensible starting values for turning, drilling and milling.
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Wet Bulb Temperature: The Heat Number That Matters Most
What wet bulb temperature measures, the Stull formula behind it, the 35 °C survival limit, and heat-stress thresholds for work and sport.
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Irregular Areas: Measuring Shapes That Aren't Rectangles
How to measure land and surfaces that aren't regular shapes: Heron's formula for triangles, the diagonal method for quadrilaterals, and polygon coordinates.
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Age Math: How Old Are You in Days, Hours and Minutes?
How exact age is calculated from a date of birth, why leap years and time zones complicate it, and what age in days is actually useful for.
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Essential Workshop Tools: A Practical Guide to What You Actually Need
Build a workshop that earns its keep: the hand tools, power tools and measuring instruments that matter, what to buy first, and how to keep everything sharp, accurate and safe.
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Homemade Glue from Polystyrene and Petrol: How It Works
Dissolve polystyrene foam in petrol and you get a capable solvent-weld adhesive. The chemistry, the step-by-step method, the right consistency, and the safety rules that matter.
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How to Calculate Your Monthly Mortgage Payment
Understand the mortgage payment formula step by step, see a worked example, and learn how rate, term and extra payments change what you pay each month.
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How Much Concrete Do You Need? A Practical Guide
Work out concrete volume for slabs, footings and columns, convert between cubic meters and yards, and order the right amount with a sensible waste allowance.
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Cooling Load Basics: How Many BTUs Does Your Room Need?
Learn the quick BTU rule of thumb for air conditioner sizing, the adjustments that matter — sun, insulation, occupants and ceiling height — and how to avoid buying an oversized unit.
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Loan EMI Explained: How Your Monthly Installment Works
What an EMI really is, how the equal-installment formula balances interest and principal, how amortization shifts over time, and how prepayment saves you money.
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Solar Panel Sizing Explained: Panels, Inverter and Batteries
Size an off-grid or backup solar system step by step: daily energy loads, sun hours, array size with losses, inverter capacity and battery storage with depth of discharge.
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Tile Math: How Many Tiles and Boxes Do You Really Need?
Calculate tile quantities the way tilers do: room area, tile coverage, a 10–15% waste allowance, and how to convert the result into boxes without over-buying.
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Percentage Shortcuts You Can Do in Your Head
Mental math tricks for percentages: the 10% anchor, the swap trick, quick tips and discounts, and how percentage change really works.
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