Undersize a pipe and your pump strains, your energy bill climbs, and the flow never reaches the far end with enough pressure. Oversize it and you've wasted money on material forever. The number that decides it all is pressure drop — the energy a fluid loses to friction as it travels through a pipe or duct. The gold-standard way to calculate it is the Darcy-Weisbach equation , and this guide gives you a free calculator that does the hard part — the friction factor via the Colebrook-White and Swamee-Jain equations — automatically and accurately. Figure 1. As fluid flows through a pipe, friction with the walls steadily drains its pressure from P₁ to P₂. The Darcy-Weisbach equation quantifies exactly how much is lost. Table of Contents The Pressure Drop / Head Loss Calculator What Are Head Loss & Pressure Drop? The Darcy-Weisbach Equation The Friction Factor (the Hard Part) Colebrook-White vs Swamee-Jain Pipe Roughness Values ...
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