Compute the drag force on a body in a fluid stream: F_D = ½·ρ·v²·C_D·A (N), where ρ is the fluid density, v the free-stream velocity, C_D the drag coefficient (shape- and Reynolds-dependent), and A the reference (frontal projected) area. A built-in shape library supplies typical high-Re C_D values: sphere 0.47, hemisphere 0.42, long cylinder 0.81, disk/flat plate 1.17, cube 1.05, streamlined airfoil 0.04, long streamlined ellipsoid 0.07, cone 0.50; or choose 'Custom' to enter C_D directly. Optionally, with dynamic viscosity μ and characteristic length L, the Reynolds number Re = ρ·v·L/μ is computed, and the power dissipated by drag P = F_D·v (W). Density in kg/m³/g/cm³, velocity in m/s/km/h, area in m²/cm²/mm², length in m/cm/mm.
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Key facts
Category
Math & Numbers
Input types
select, number
Output type
json
Sample coverage
4
API ready
Yes
Overview
Calculate the drag force on a body in a fluid stream using F_D = ½·ρ·v²·C_D·A. Enter fluid density, velocity, drag coefficient, and frontal reference area to get force in newtons, plus drag power in watts. Add dynamic viscosity and characteristic length to calculate the Reynolds number.
When to use
Estimate aerodynamic drag on objects moving through air.
Calculate hydrodynamic drag on bodies in water or another fluid.
Compare the effect of shape, velocity, density, or frontal area on drag force.
How it works
1Choose a preset shape to use its typical high-Reynolds-number drag coefficient, or select Custom and enter C_D directly.
2Enter fluid density, free-stream velocity, and frontal reference area, selecting the appropriate units.
3The calculator converts the inputs and applies F_D = ½·ρ·v²·C_D·A to return drag force in newtons.
4Optionally enter dynamic viscosity and characteristic length to calculate Re = ρ·v·L/μ; drag power is also calculated as P = F_D·v.
Use cases
Aerodynamic estimates for vehicles, spheres, airfoils, and other bodies in air.
Hydrodynamic calculations for submerged objects moving through water.
Early-stage fluid mechanics comparisons using different shapes and reference areas.
Examples
1. Sphere moving through air
Engineering student
Background
A student wants to estimate the drag on a 1 m² sphere moving through air at 20 m/s.
Problem
Calculate the drag force and power using the typical sphere coefficient.
How to use
Select Sphere, enter C_D = 0.47, density = 1.225 kg/m³, velocity = 20 m/s, and reference area = 1 m².