calculators.dev

Practical project calculators

Calculators that finish the job.

Fast, accurate calculators for real projects — concrete, RV power, garden beds, deadlines. The number, the materials, and what to do next.

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Construction & DIYConcrete Slab CalculatorCalculate concrete for a slab: cubic yards (or m³), the number of 80-lb bags including waste, and an optional cost. Set the length, width, thickness, and waste %.
Date & TimeDays Between DatesCount the exact number of days between two dates, with an inclusive/exclusive toggle and a weeks-and-days breakdown.
Date & TimeDate Calculator (Add or Subtract Time)Add or subtract years, months, weeks, and days from any date. Handles month-end clamping (Jan 31 + 1 month → Feb 28) and shows the resulting day of the week.
Date & TimeBusiness Days CalculatorCount the business (working) days between two dates. Inclusive of both endpoints, excluding weekends and observed US federal holidays.
Date & TimeAge CalculatorCalculate exact age in years, months, and days from a birth date as of today or any chosen date. Shows total days, weeks, and months plus a countdown to the next birthday.
Date & TimeDays Until a Date CalculatorCount the days until a future date from today or any starting date. Shows a signed count, so past dates read as 'X days ago' and today reads as 0.

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Shown, not hidden
The formula, assumptions, and a worked example are on every page — no black box.
Fast & ad-light
Static pages, client-side math, minimal JavaScript. The tool loads first.
Developer-built & tested
Every formula ships with unit tests; the worked example is the literal fixture.