Recovery System Calculator
Size your rocket parachute for a safe descent rate. Calculates canopy diameter, area, landing energy, and drift distance using aerodynamic drag equations.
About this calculator
This calculator sizes a single recovery parachute by solving the terminal-velocity drag equation for diameter: at a steady descent rate, drag force exactly balances weight (mg = 0.5 × ρ × v² × Cd × A), which rearranges to D = sqrt(8mg / (π × ρ × Cd × v²)). It adjusts air density for your launch site's altitude above sea level using the barometric formula (ρ = ρ₀ × e^(−altitude / 8500m)), since thinner air at higher elevations means you need a larger canopy to generate the same drag — a detail that's easy to overlook when sizing a chute using a sea-level rule of thumb. The drag coefficient itself comes from your chosen chute geometry: 1.5 for a hemispherical chute (the most common design), 0.8 for a flat or cruciform chute, and 0.4 for a lightweight streamer, reflecting how much less drag a streamer generates per unit area compared to a full canopy.
From the resulting diameter it derives canopy area in both metric and imperial units, landing kinetic energy (0.5 × mass × velocity²) to flag whether your descent rate keeps impact energy under the commonly-cited 75 J damage threshold, and a rough estimate of descent time and downwind drift assuming a flat 5 m/s average wind — a placeholder, not a wind-forecast input, so treat the drift figure as a rough order of magnitude rather than a landing-zone prediction. Note this models a single-parachute recovery system only; for staged drogue-then-main recovery, this calculator's sibling dual-deploy tool handles sizing both canopies together.
Inputs
Results
Parachute diameter (cm)
52.1
How to Use This Calculator
- Enter Rocket mass (kg), Target descent rate (m/s), and Launch site altitude (m MSL).
- Select the Parachute type.
- Review the Parachute diameter (cm) result.
- Use Parachute diameter (in) and Canopy area (m²) to inform your decision.
How the result changes with Target descent rate (m/s)
| Target descent rate (m/s) | Parachute diameter (cm) |
|---|---|
| 2.5 | 104.3 |
| 3.75 | 69.5 |
| 7.5 | 34.8 |
| 13 | 20.1 |
What each input means
- Rocket mass (kg)
- Total mass of the rocket at recovery (after motor burnout, propellant expended).
- Target descent rate (m/s)
- Desired descent speed. 3-5 m/s is typical for safe recovery; 5-8 m/s for drogue chutes.
- Launch site altitude (m MSL)
- Elevation above sea level. Higher altitudes have thinner air, requiring larger chutes.
- Parachute type
- Parachute geometry, which sets the drag coefficient used for sizing.
What each result means
- Parachute diameter (cm)
- Required canopy diameter for the target descent rate.
- Parachute diameter (in)
- Diameter in inches for US-sourced chutes.
- Canopy area (m²)
- Projected canopy area.
- Landing kinetic energy (J)
- Impact energy at landing. Keep below 75 J to avoid damage.
- Descent time (s)
- Estimated time from apogee to ground.
- Wind drift estimate (m)
- Approximate downwind drift assuming 5 m/s average wind.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersRocket mass (kg) = 0.5, Target descent rate (m/s) = 5, Launch site altitude (m MSL) = 0, Parachute type = 1 = 4 input(s) provided
- Calculate Parachute diameterParachute diameter = diameterM * 10052.1 = 52.1
- Calculate Parachute diameterParachute diameter = diameterM * 39.370120.5 = 20.5
- Calculate Canopy areaCanopy area = π * (diameterM / 2) ^ 20.213 = 0.213
Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does my launch site's altitude change the required parachute size?
Air density drops with altitude following the barometric formula the calculator uses (ρ = ρ₀ × e^(−altitude / 8500m)), and a lower-density atmosphere generates less drag for a given canopy size and speed. Since the diameter formula divides by air density, a higher launch-site elevation directly pushes the required diameter up to compensate for the thinner air.
What does changing the parachute type actually affect?
It swaps the drag coefficient (Cd) used in the sizing formula: 1.5 for hemispherical (the most common canopy shape), 0.8 for flat or cruciform, and 0.4 for a streamer. Because Cd sits in the denominator of the diameter equation, the lower-drag streamer needs a much larger surface area — or in practice a longer streamer — to achieve the same descent rate as a hemispherical chute.
How reliable is the wind drift estimate?
It's a placeholder calculation, not a wind forecast: the code multiplies your descent time by a fixed assumed average wind speed of 5 m/s regardless of what the input form otherwise asks. Treat the drift figure as a rough order-of-magnitude sense of how far you might need to search after landing, not a prediction tied to actual local wind conditions on launch day.
How is this different from the dual-deploy calculator?
This calculator sizes one single parachute for the entire descent from apogee to the ground using one target descent rate. The dual-deploy calculator instead sizes two separate canopies — a fast drogue chute deployed at apogee and a slower main chute deployed lower down — for rockets using a staged recovery sequence.
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