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Long Division

Every step of the division bracket, with the multiplication you need shown right when you need it.

Long Division with 2-Digit Divisors

The harder version — estimating the quotient when the divisor has two digits.

Dividing Decimals

Move the decimal point in the divisor first — then it is ordinary long division.

Fraction to Decimal

A fraction is a division problem. Divide the top by the bottom and watch it turn into a decimal.

Long Multiplication

Including the placeholder zero on the second row — the step almost every kid forgets.

Multiplying Decimals

Multiply as if the points were not there, then count the places to put the point back.

Area Model (Box Method)

The method your child is taught at school and you probably were not. Split by place value, multiply, add.

Multiply & Divide by 10, 100, 1000

Watch the decimal point slide. It never was about “adding zeros”.

Grades 2–4

Addition with Carrying

Column addition with the carried digits written where they actually go.

Grades 2–4

Subtraction with Borrowing

Regrouping shown the way it is written on paper — crossed out, with the new number above.

Subtracting Across Zeros

When the neighbour is a zero it has nothing to lend, so you keep going left. The hardest one in the unit.

Adding Decimals

Line up the points, fill the gaps with zeros, then add like normal.

Subtracting Decimals

The same lining-up rule, plus borrowing across the decimal point.

Adding & Subtracting Fractions

Unlike denominators, with the common denominator found by counting multiples — the step that is normally invisible.

Multiplying Fractions

Cancel diagonally first, then multiply straight across. No common denominator needed.

Dividing Fractions

Keep, change, flip — and this one actually shows you why flipping works.

Subtracting Mixed Numbers

Borrowing a whole one and turning it into fraction pieces. The hardest thing in the fraction unit.

Simplifying Fractions

Find the greatest common factor from the actual factor lists, then divide once.

Mixed & Improper Fractions

Both directions, with a picture of why the whole number turns into pieces.

Comparing Fractions

Which one is bigger? Cross multiply, and see both drawn as bars.

Equivalent Fractions

The same amount written five different ways, drawn side by side so you can see it is the same.

Fraction, Decimal & Percent

All three are the same number. This shows how to walk between them.

Prime Factorization

A factor tree that grows branch by branch, with the reason each prime was chosen.

Greatest Common Factor (GCF)

The ladder method — divide both numbers together until nothing is left in common.

Least Common Multiple (LCM)

Same ladder as the GCF, but you multiply in an L shape — down the side and along the bottom.

Divisibility Rules

Test one number against every rule at once, and see why each one works.

Factor Pairs

Every pair that multiplies to your number — and why you only test up to the square root.

Order of Operations (PEMDAS)

One operation at a time, with the reason that one goes next. Brackets, exponents, then × ÷, then + −.

Evaluating Expressions

Put a number in for x, then work through it in the right order.

Two-Step Equations

Undo the addition first, then the multiplication — doing the same thing to both sides every time.

Adding & Subtracting Integers

Walk it out on a number line — including why subtracting a negative moves you right.

Percent of a Number

What is 15% of 80? Turn the percent into a decimal, then multiply — with a 10% sanity check.

Percent Increase & Decrease

The trap is what goes on the bottom. It is always the number you started with.

Solving Proportions

Two ratios that match, one number missing. Cross multiply and it falls out.

Unit Rate

Cost for one. Once everything is “per 1” you can compare any two deals.

Metric Conversions

The metric staircase. Every step is ten, so converting is just sliding the decimal point.

Customary Conversions

Inches, feet, pounds, cups. No pattern to lean on — so go down to the smallest unit and back up.

Elapsed Time

Count on to the next whole hour, then the hours, then the leftover minutes. Works every time.

Grades 3–6

Perimeter & Area

The two get mixed up constantly. One is the walk around the edge, the other is the space inside.

Area of Composite Figures

An L-shape is just two rectangles. Slice it, do each piece, add them up.

Volume of a Rectangular Prism

One layer of cubes, then stack the layers. That is all volume ever is.

Angles

See the angle drawn, name it, and find what it pairs with to make 90° or 180°.

Mean, Median, Mode & Range

Mean, median and mode from one sorted list — plus the range, which measures spread rather than average.

Rounding on a Number Line

“Five or more, round up” is a picture before it is a rule. Here is the picture.

Grades 2–4

Place Value & Expanded Form

The same digit is worth a different amount depending on where it sits.

Roman Numerals

Built one letter at a time, with the subtractive pairs like IV and CM explained as they appear.

Estimating

Round first, work it out in your head, then check the real answer is close.

Absolute Value

Not “make it positive” — it is the distance from zero, and distance is never negative.

Ratio Tables

Scale both columns by the same amount and the ratio survives. That is the whole idea.

Money

Mortgage Calculator

Your monthly payment, and the two scenarios side by side — scheduled, and with extra principal.

Money

Loan Calculator

The monthly payment, what the fee does to the real rate, and the two payoff schedules side by side.

Grades & GPA

Final Grade Calculator

What you need on the final — and whether it is actually reachable.

Grades & GPA

GPA Calculator

Your weighted GPA, and exactly what next term has to look like to move it.

Work & time

Hours Calculator

Hours worked, what the unpaid break really costs, and where overtime starts.

Work & time

Time Calculator

Add times, subtract times, or measure the gap between two of them.

Dice Roller

Roll anything, and see how likely the number you just got actually was.

Random Number Generator

Pick numbers in a range — with or without repeats.

Basic Calculator

The plain four-function calculator — plus what your answer looks like in other forms.

Scientific Calculator

Type a whole expression. Trig, logs, powers, roots and factorials.

Mulch Calculator

Find out how much mulch you need in cubic yards or bags. Includes weight, delivery loads, and cost — with adjustable density.

Topsoil Calculator

Calculate topsoil in cubic yards or bags for lawns, beds and raised beds. Shows weight, delivery loads and cost.

Gravel Calculator

Calculate gravel in cubic yards or tons for driveways, paths and drainage. Includes depth guidance and weight per load.

Sand Calculator

Work out how much sand you need in cubic yards, tons or bags. Includes paver bedding depth and weight per load.

Compost Calculator

Calculate compost in cubic yards or bags for lawns, garden beds and raised beds, with depth guidance and weight.

River Rock Calculator

How much river rock you need in cubic yards or tons, with recommended depth and weight per load.

Crushed Stone Calculator

Crushed stone calculator for base layers under pavers, driveways and slabs. Yards, tons, weight and depth guidance.

Concrete Slab Calculator

Calculate concrete for a slab in cubic yards and bags. Shows bag counts for 40, 60 and 80 lb bags plus the ready-mix threshold.

Paver Base Calculator

Calculate the crushed stone base and sand bedding for a paver patio or walkway, including compaction allowance.

Sod Calculator

Calculate how much sod you need in pallets and rolls. Covers cool-season rolls and warm-season slabs, with pallet weight.

Grass Seed Calculator

Grass seed calculator with seeding rates per 1,000 sq ft for fescue, bluegrass, ryegrass, bermuda and zoysia — new lawn and overseeding.

Fertilizer Calculator

Lawn fertilizer calculator. Converts a target nitrogen rate and your bag N-P-K into pounds of product for your lawn size.

Fence Calculator

Fence calculator for posts, sections, rails and concrete. Works for wood, vinyl and chain link at any post spacing.

Retaining Wall Calculator

Retaining wall block calculator. Gives block count by course, cap blocks and base stone for segmental block walls.

Paver Calculator

Paver calculator for patios, walkways and driveways. Paver count by size with waste allowances for running bond, diagonal and herringbone.

Plant Spacing Calculator

Plant spacing calculator for ground cover, shrubs and bedding plants. Staggered and square grid layouts with plant counts.

Concrete Footing Calculator

Concrete footing calculator for round tube forms and square footings. Bag count, cubic yards and weight from diameter, depth and quantity.

Concrete Steps Calculator

Concrete steps calculator. Volume, bags and cubic yards for poured steps, using the correct stacked-slab formula.

Rebar Calculator

Rebar calculator for slab grids. Bar count each way, total linear feet, sticks to buy and number of intersections to tie.

Asphalt Calculator

Asphalt calculator for driveways and paths. Tons and cubic yards from area and compacted thickness, with adjustable density.

Excavation Calculator

Excavation calculator. Cubic yards of soil to remove, weight, and haul-away loads — including the swell that catches people out.

Tile Calculator

Tile calculator for floors and walls. Tile count by size with waste for diagonal and herringbone layouts, plus thinset and grout.

Thinset Calculator

Thinset mortar calculator. Bag count by trowel notch size for standard and large-format tile.

Grout Calculator

Tile grout calculator. Pounds of grout by tile size and joint width, with sanded versus unsanded guidance.

Paint Calculator

Paint calculator for interior walls. Gallons by wall area and coats, with door and window openings subtracted.

Ceiling Paint Calculator

Ceiling paint calculator. Gallons by room area and coats, with coverage guidance for flat and textured ceilings.

Drywall Calculator

Drywall calculator for sheets, screws, joint compound and tape. Subtracts door and window openings automatically.

Joint Compound Calculator

Drywall joint compound calculator. Gallons and boxes by wall area and finish level, based on USG published coverage.

Flooring Calculator

Flooring calculator for laminate, LVP and hardwood. Box count by coverage with waste for plank layout.

Carpet Calculator

Carpet calculator in square yards and square feet, with padding, and guidance on roll width and seam placement.

Baseboard Calculator

Baseboard and trim calculator. Linear feet and stick count with waste for miter cuts.

Wallpaper Calculator

Wallpaper calculator with realistic roll yield. Accounts for pattern repeat and trim waste on single and double rolls.

Underlayment Calculator

Floor underlayment calculator. Roll count for laminate, LVP and engineered floors, including seam overlap.

Subfloor Calculator

Subfloor calculator for plywood and OSB sheets, including screws and subfloor adhesive tubes.

Stain Calculator

Deck and wood stain calculator. Gallons by area, coats and coverage — with the real numbers for rough and weathered wood.

Primer Calculator

Primer calculator for walls and ceilings. Gallons by area and coats, with door and window openings removed.

Crown Molding Calculator

Crown molding calculator. Linear feet and piece count from room perimeter, with realistic waste for compound mitre cuts.

Caulk Calculator

Caulk calculator. Tubes needed from linear feet and bead diameter, derived from the 10.1 oz cartridge volume.

Epoxy Floor Calculator

Garage floor epoxy calculator. Gallons and kits from area and dry film thickness in mils, with the coverage formula shown.

Roof Pitch Calculator

Roof pitch calculator. Converts rise over run into degrees, slope factor and true roof area from the building footprint.

Roofing Shingles Calculator

Shingle calculator in squares and bundles. Three bundles per square, with waste guidance for hips, valleys and starter course.

Roof Underlayment Calculator

Roof underlayment calculator for 15 lb felt, 30 lb felt and synthetic. Roll count including overlap.

Ice Barrier Calculator

Ice and water shield calculator. Roll count for eave coverage and valleys, with code coverage guidance.

Ridge Cap Calculator

Ridge cap shingle calculator. Bundle count for ridges and hips, with ridge vent allowance.

Gutter Calculator

Gutter calculator for length, hangers, end caps and downspout count based on roof drainage area.

Siding Calculator

Siding calculator in squares and boxes for vinyl, fiber cement and lap siding, with openings subtracted.

Soffit Calculator

Soffit and fascia calculator. Panel area from overhang width and eave length, with vented panel guidance.

Stucco Calculator

Stucco calculator. Bags of mix from wall area and coat thickness, with doors and windows subtracted.

Fascia Calculator

Fascia calculator. Linear feet, board count, drip edge and nails for roof edge trim from the total run.

Driveway Sealer Calculator

Driveway sealer calculator. Gallons and 5-gallon pails from area and coats, with realistic coverage for rough and porous surfaces.

Board Foot Calculator

Board foot calculator for lumber. Converts thickness, width, length and quantity into board feet and cost.

Lumber Weight Calculator

Lumber weight calculator by board feet. Estimates weight for pine, fir, oak and pressure-treated lumber.

Deck Board Calculator

Deck board calculator. Board count by width and length with gap spacing, plus deck screws.

Deck Joist Calculator

Deck joist calculator. Counts joists and hangers at 12, 16 or 24 inch spacing for a given deck width.

Deck Railing Calculator

Deck railing calculator for posts, rails and balusters with the 4 inch sphere rule spacing.

Stair Calculator

Stair stringer calculator. Riser height, tread count, total run and stringer length from total rise.

Plywood Calculator

Plywood and OSB sheet calculator. Sheet count by area for sheathing, subfloor and cabinet work.

Fence Picket Calculator

Fence picket calculator. Board count for privacy and spaced picket fences by run length and picket width.

Miter Angle Calculator

Miter angle calculator for frames and boxes. Saw setting and interior angle for any number of sides, from triangles to twenty-sided rings.

Compound Miter Calculator

Compound miter calculator. Miter and bevel angles for canted boxes, hoppers, planters and crown molding, with the trigonometry shown.

Cut List Calculator

Cut list calculator. Pieces per board and boards needed from stock length, piece length and saw kerf.

Wood Movement Calculator

Wood movement calculator. Shrinkage and swelling in inches by species, cut and moisture change, using USDA Wood Handbook coefficients.

Panel Glue Up Calculator

Panel glue up calculator. Board count, glue joints and glue line length for a solid wood panel, allowing for jointing loss.

Mortise and Tenon Calculator

Mortise and tenon calculator. Tenon thickness, shoulder size and mortise depth from stock dimensions using the one-third rule.

Shelf Spacing Calculator

Shelf spacing calculator. Clear height per opening from cabinet height, shelf thickness and shelf count.

Table Seating Calculator

Table seating calculator. Seats for rectangular and round tables from size and place setting width, with room clearance.

Segmented Ring Calculator

Segmented ring calculator. Miter angle, inner and outer segment lengths and stock required for a segmented circle.

Wood Finish Calculator

Wood finish calculator. Ounces and quarts of oil, polyurethane, shellac or lacquer from surface area and coat count.

Insulation Calculator

Insulation calculator for fiberglass batts and rolls. Bag count by area with R-value and cavity depth guidance.

Blown Insulation Calculator

Blown-in attic insulation calculator. Bag count by target R-value for cellulose and loose-fill fiberglass.

Stud Calculator

Wall stud calculator. Counts studs and top and bottom plates by wall length and stud spacing.

Vapor Barrier Calculator

Vapor barrier calculator. Roll count for 6 mil and 10 mil poly with overlap allowance for crawl spaces and slabs.

House Wrap Calculator

House wrap calculator. Roll count for 3 ft and 9 ft wide weather-resistive barrier including overlap.

Brick Calculator

Brick calculator. Brick count per square foot by brick size, plus mortar bags and sand.

Concrete Block Calculator

Concrete block calculator. CMU count per square foot with mortar bags and core fill volume.

Mortar Calculator

Mortar calculator. Bag count for brick and block laying, with sand quantities for site-mixed mortar.

Filament Weight Calculator

Filament weight and length calculator for 3D printing. Grams to metres by material density, for 1.75, 2.85 and 3.00 mm filament.

Filament Remaining Calculator

Filament remaining calculator. Length and weight left on a partly used spool from outer diameter, core diameter and winding width.

Steps Per mm Calculator

Steps per mm calculator for 3D printers and CNC. Belt-driven and leadscrew axes from motor steps, microstepping, pulley teeth and screw pitch.

Belt Length Calculator

Timing belt length calculator. Closed loop length and tooth count from pulley teeth and centre distance, for GT2, GT3 and HTD belts.

Layer Height Calculator

Layer height calculator for 3D printing. Finds the magic numbers that divide evenly into the Z axis full-step distance.

Extrusion Multiplier Calculator

Extrusion multiplier and flow rate calculator. Corrects flow from a measured single-wall thickness against the expected extrusion width.

Print Scale Calculator

Print dimensional accuracy calculator. Scale percentage and corrected steps per mm from a measured versus intended dimension.

Tap Drill Size Calculator

Tap drill and clearance hole size calculator for metric and UNC threads, with the formula and ISO 273 clearance sizes.

Baker's Percentage Calculator

Baker's percentage calculator. Water, salt and yeast weights from hydration and salt percentages, or back-calculated from total dough weight.

Pan Size Conversion Calculator

Cake pan size conversion calculator. Scale factor between round, square and rectangular pans by area, with depth and bake time guidance.

Recipe Scaling Calculator

Recipe scaling calculator. Multiplier from original to desired servings, with per-ingredient conversion and notes on what does not scale linearly.

High Altitude Baking Calculator

High altitude baking calculator using Colorado State Extension adjustment bands. Baking powder, sugar, liquid and oven temperature by elevation.

Cake Serving Calculator

Cake serving calculator. Servings from round, square and sheet pans at party and event portion sizes, plus batter volume.

Pizza Dough Calculator

Pizza dough calculator using thickness factor. Dough ball weight in ounces and grams for any pizza diameter, plus flour and water by hydration.

Sourdough Starter Calculator

Sourdough starter calculator. Feeding ratios and levain builds by weight, with hydration and discard amounts.

Oven Temperature Converter

Oven temperature converter. Fahrenheit, Celsius, gas mark and fan-assisted equivalents, with the standard fan reduction.

Tire Size Calculator

Tire size comparison calculator. Overall diameter, circumference, revolutions per mile and speedometer error between two tire sizes.

Gear Ratio Calculator

Gear ratio calculator. Engine RPM from road speed, axle ratio, transmission ratio and tire diameter, or road speed from RPM.

Axle Ratio Calculator

Axle ratio calculator for a tire size change. Finds the new gear ratio that restores the original engine rpm at road speed.

Engine Displacement Calculator

Engine displacement calculator from bore, stroke and cylinder count. Results in cc, litres and cubic inches, with overbore comparison.

Compression Ratio Calculator

Compression ratio calculator from bore, stroke, chamber volume, gasket thickness, piston dish and deck clearance.

Wheel Offset Calculator

Wheel offset and backspacing calculator. Converts between the two and shows inboard and outboard movement against your current wheel.

Torque and Horsepower Calculator

Torque and horsepower calculator. Converts between hp, lb-ft and rpm, with metric kW and Nm equivalents.