Calculators that show their work.
Lbaro is a growing collection of free calculators for building projects, school, science, fitness tests and personal finance. Every tool explains the formula behind the answer, links to official sources, and runs right in your browser with no sign-up.
Construction & Landscaping
See allCubic Yard CalculatorTurn the length, width and depth of any bed, trench or hole into cubic yards, then price the order before you call the supplier.Gravel CalculatorWork out the volume, weight and cost of gravel for a driveway, path, patio or drainage trench, with densities for the most common stone types.Square Footage CalculatorAdd up the area of one room or a whole floor plan, subtract what you will not cover, and see the result in square feet, square meters and square yards.Concrete CalculatorEstimate how much concrete to order for a slab, footing, post hole or set of steps, and how many premixed bags that would take.
Math
See allRatio CalculatorSimplify any ratio, find a missing term, scale a recipe or mix, or divide an amount in a given ratio, with the working shown.Proportion CalculatorSolve a/b = c/d for any missing value with cross multiplication, and check whether two ratios are really in proportion.GCF CalculatorEnter two or more whole numbers to get their greatest common factor, least common multiple, prime factorizations and the Euclidean algorithm worked out.
School & Test Scores
See allAP Lang Score CalculatorEnter your multiple-choice result and your three essay scores to estimate your AP English Language and Composition score on the 1–5 scale.APUSH Score CalculatorPlug in your multiple-choice, short-answer, DBQ and LEQ results to estimate your AP United States History score from 1 to 5.Final Grade CalculatorFind out exactly what you need on the final exam to finish with the grade you want, and see the score needed for every letter grade.
Science
See allFitness & Assessment
See allUSMC PFT CalculatorScore your Marine Corps Physical Fitness Test by age group and sex, with event points, total score, class and pass or fail.Chronological Age CalculatorGet a child's exact age on the test date in years, months and days, the way assessment manuals calculate it, plus corrected age for babies born early.
Personal Finance
See allLatest guides
All guides
How to Scale a Recipe Up or Down Using ProportionsDouble, halve or resize any recipe with a single scaling factor. Includes conversions for awkward amounts, tips for eggs and spices, and pan size adjustments.
Cooking with Ratios: Bread, Rice, Coffee and Vinaigrette Without a RecipeLearn the classic kitchen ratios for bread, pie crust, rice, coffee and dressings, and how to scale them up or down for any batch size.
Concrete for Footings and Post Holes: Sizes, Depth and VolumeCalculate concrete for deck footings, fence posts and continuous footings. Covers frost depth, form tubes, hole sizes and how to total many holes at once.
Square Feet to Square Meters (and Yards, Acres): Conversions and ChartsConvert square feet to square meters, square yards, acres and hectares with exact factors, quick charts and tips to avoid the most common area-conversion mistakes.
Tons vs. Cubic Yards of Gravel: How to Convert and Compare PricesHow many tons are in a yard of gravel, how to convert between tons and cubic yards, and how to compare quotes from suppliers that price differently.
How Much Topsoil Do I Need? Raised Beds, New Lawns and LevelingCalculate topsoil for raised beds, new lawns and low spots, plan for settling, and choose between topsoil, garden mix and fill dirt.