Calculators — Guides & Articles

• Design Pressure vs Test Pressure: Convert Units Right

  Published 2026-08-14

  Design pressure vs test pressure: what each term means, why test pressure is higher, and how to convert values between bar, psi, kPa and other units.

  

• How to Calculate Your Pregnancy Due Date

  Published 2026-08-14

  Estimate your due date with Naegele's rule — add 280 days to your last period, adjust for your cycle length, and read EDD and gestational age instantly.

  

• How to Calculate PPI and DPI: What Bonds the Terms

  Published 2026-08-14

  Calculate PPI and DPI from any screen's resolution and diagonal size. See the formula, the bond between the two terms, and a step-by-step method.

  

• 3D Bin Packing Calculator: When Scalar Packing Helps

  Published 2026-08-13

  3D bin packing calculator: see when a scalar First Fit Decreasing model fits your problem, how to run it on this site, and the limits of 1D packing.

  

• What Affects Your Real BAC Beyond the Widmark Formula

  Published 2026-08-13

  Drinks, weight, sex, and hours are not the whole picture. Here is what the Widmark formula leaves out and what moves your real BAC reading.

  

• How to Determine Newborn Eye Color Step by Step

  Published 2026-08-13

  Determine your newborn's eye color from both parents' eyes using a simple calculator that turns published genetics charts into brown, green, and blue odds.

  

• How to Calculate Average Rate of Change Step by Step

  Published 2026-08-13

  Calculate the average rate of change with a clear formula and the free Average Calculator. Average one slope or many interval rates in real time.

  

• How to Convert Area to Gallons: Add Depth First

  Published 2026-08-12

  Area to gallons isn't a single step. Multiply area by depth for volume, then convert the cubic result using exact factors and a worked example inside.

  

• How to Convert Angle to Slope: Formula and Method

  Published 2026-08-12

  Convert an angle to a slope ratio or percent grade with the tangent formula. The Angle Converter handles the degree-to-radian step so tan(θ) gives you the…

  

• Accurate Age Calculator: Years, Months, and Days

  Published 2026-08-12

  An accurate age calculator counts full years, months, and days from your date of birth. See what makes the math reliable and use the free tool.