Parachute Size Calculator (Drag)

Model rocket recovery depends on choosing the right parachute size — too small and your rocket hits the ground hard, too large and it drifts into the next county. Enter your Rocket Recovery Mass, Desired Descent Velocity, Parachute Shape, and Air Density into the Parachute Size Calculator to get the Required Parachute Diameter. Secondary outputs include the Drag Coefficient, Reference Area, and Actual Descent Rate.

g

Total weight of rocket at recovery including parachute

m/s

Target descent speed for safe recovery

Shape affects drag coefficient

%

Percentage of parachute diameter for spill hole (improves stability)

kg/m³

Standard sea level: 1.225 kg/m³

Results

Required Parachute Diameter

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Drag Coefficient (Cd)

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Reference Area

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Actual Descent Rate

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Frequently Asked Questions

How fast should a rocket descend on a parachute?

For model rockets, the ideal descent rate is between 3-6 m/s (10-20 ft/s). This provides safe recovery while preventing damage to the rocket or surroundings.

What is the drag coefficient (Cd) for different parachute shapes?

Flat circular parachutes have Cd ≈ 1.3-1.5, hexagonal (parasheet) Cd ≈ 1.2-1.4, hemispherical Cd ≈ 1.2-1.3, and conical parachutes Cd ≈ 0.7-0.9. The calculator automatically applies appropriate coefficients.

Should I include a spill hole in my parachute?

A spill hole of 10-20% of the parachute diameter improves stability and reduces oscillation during descent. It slightly increases descent rate but provides more controlled landing.

How does altitude affect parachute performance?

Higher altitudes have lower air density, requiring larger parachutes for the same descent rate. At 3000m altitude, air density is about 0.9 kg/m³ compared to 1.225 kg/m³ at sea level.

What is reference area in parachute calculations?

Reference area is the projected area of the parachute perpendicular to the direction of descent. It's used in drag calculations and differs from the actual fabric area of the parachute.

Can I use this calculator for different rocket sizes?

Yes, this calculator works for any model rocket weight from small rockets (10g) to large high-power rockets (5kg). Adjust the recovery mass to include the parachute and recovery system weight.