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Fluid Drag Force, Coefficient & Area

Calculate positive drag force from fluid density, relative speed, drag coefficient and its matching reference area.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

Density 1.2 kg/m³, relative speed 10 m/s, coefficient 0.5 and reference area 2 m² give a drag force of 60 N.

Drag force = ½ × density × relative speed² × drag coefficient × reference area

Worked example

Enter these known values and leave the other values blank.

Fluid density
1.2 kg/m³
Relative flow speed
10 m/s
Drag coefficient
0.5
Coefficient reference area
2 m²
Drag force magnitude
60 N

Assumptions and limitations

  • All five quantities are strictly positive in this model. Speed is relative to the fluid, not necessarily relative to the ground.
  • Use the same reference-area convention that was used to define the coefficient. Frontal area, wetted area and wing planform area are not interchangeable without adjusting the coefficient.
  • A supplied coefficient applies to particular geometry, orientation and flow conditions, including Reynolds and Mach numbers. Holding it fixed while changing speed is an assumption.

Common questions

Does doubling speed quadruple drag?

It does if density, coefficient and reference area remain fixed. In a real flow, the coefficient may change with speed.

Can the calculator predict the drag coefficient from shape alone?

No. It relates a supplied coefficient to the other quantities; it does not replace measured data or a suitable aerodynamic model.

References

Bookify uses exact customary mass and volume definitions for density units, replacing rounded factors in the reference. The pound-force uses the exact international pound and standard gravity instead of the rounded captured factor.

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