Calculator Guides
Step-by-step guides with formulas, examples, and tips for every calculation.
How much concrete do I need?
Multiply length × width × depth (in feet) and divide by 27 to get cubic yards. A 10×10 slab 4 inches thick needs 1.23 cu...
How do I calculate a percentage?
To find X% of Y, multiply Y by X and divide by 100. For example, 15% of 200 = 200 × 15 ÷ 100 = 30. To find what percent ...
How is a monthly mortgage payment calculated?
Your monthly payment is calculated using the formula M = P × [r(1+r)^n] / [(1+r)^n - 1], where P is the loan amount, r i...
How do I use a scientific calculator?
A scientific calculator handles advanced math: trigonometry (sin, cos, tan), logarithms (log, ln), exponents, roots, and...
How do I calculate my BMI?
BMI = weight (lbs) × 703 ÷ height (inches)². A person who is 5’9″ and 165 lbs has a BMI of 24.4, which is in the normal ...
How does compound interest work?
Compound interest earns interest on your interest. With $10,000 at 7% compounded annually, you’ll have $19,672 after 10 ...
How do I calculate my overall grade?
Multiply each assignment score by its weight percentage, add them together, then divide by the total weight. If homework...
How do I calculate monthly loan payments?
Use the formula M = P × [r(1+r)^n] / [(1+r)^n - 1]. For a $25,000 loan at 5% for 5 years, r = 0.05/12 = 0.004167 and n =...
How many calories should I eat per day?
It depends on your age, weight, height, and activity level. A 30-year-old male, 5’9″, 165 lbs, moderately active needs a...
How do I add fractions with different denominators?
Find the least common denominator (LCD), convert both fractions to equivalent fractions with that denominator, then add ...
How do I calculate square footage?
Multiply length × width in feet. A 12×15 room is 180 square feet. For irregular shapes, divide into rectangles, calculat...
How much should I tip?
The standard tip is 15–20% of the pre-tax bill. On a $50 bill, a 20% tip is $10, making the total $60. For excellent ser...
How old am I exactly?
To calculate your exact age, subtract your birth date from today’s date. Born January 15, 1990? As of March 26, 2026, yo...
How do you calculate board feet?
Board feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12. A standard 2×4×8’ board has 5.33 board feet....
How many sheets of drywall do I need?
Divide total wall area (in square feet) by 32 for 4×8 sheets or 48 for 4×12 sheets, then add 10% for waste. A 12×12 room...
How do I calculate fence materials?
For a 100-foot privacy fence 6 feet tall: you need 18 posts (one every 6 feet, including both ends), 51 rails (3 per sec...
How much mulch do I need?
Multiply length × width × depth (in feet) and divide by 27 for cubic yards. A 20×10 garden bed with 3 inches of mulch ne...
How much gravel do I need?
Multiply length × width × depth (in feet) and divide by 27 for cubic yards. A 10×20 driveway with 4 inches of gravel nee...
How much paint do I need?
One gallon of paint covers about 350 square feet per coat. For a 12×12 room with 8-foot ceilings, you need about 2 gallo...
How many shingles do I need for my roof?
Measure your roof area in square feet, divide by 100 to get roofing squares, then multiply by 3 for shingle bundles. A 2...