Parachute Size Calculator
Enter the mass coming down, the landing speed you want and the canopy shape. The calculator works out the canopy area and diameter from the drag formula, the landing energy and the size for half the speed.
- Parachute diameter
- Canopy area
- Landing speed
Model rockets usually land at 3.5 to 4.5 m/s. Fragile payloads need slower.
A parachute balances weight with drag. The canopy area is 2mg ÷ (air density × drag coefficient × speed²). A 500 g model rocket landing at 4 m/s under a dome canopy needs about 0.33 m², a parachute about 65 cm across. A flat sheet canopy of the same speed needs to be much bigger.
Parachute size chart
Dome canopy, 4 m/s. Search for a mass.
| Mass (g) | Area (m²) | Diameter (cm) | Diameter (in) |
|---|---|---|---|
| 50 | 0.033 | 21 | 8.1 |
| 100 | 0.067 | 29 | 11.5 |
| 250 | 0.167 | 46 | 18.1 |
| 500 | 0.334 | 65 | 25.7 |
| 1000 | 0.667 | 92 | 36.3 |
| 2000 | 1.335 | 130 | 51.3 |
| 5000 | 3.337 | 206 | 81.1 |
Diameter of a round canopy.
Mass and diameter
Dome canopy, 4 m/s. Slide the mass.
The canopy is drawn to scale above its payload.
How to size a parachute
Mass to diameter. Step through it.
Mass
Everything coming down.
Spill holes in the top steady the descent and cut drift, but add a little area to make up for them.
Dome, flat round or cross
Canopy shapes. Compare them.
Curved.
Simple.
Very stable.
A dome canopy is the most efficient, but flat and cross canopies are much easier to make.
Before you fly
Recovery checks. Tick each item.
Tick each item as you go.
Pack the parachute loosely with wadding so it does not melt or tangle.
What you get
Parachute sizing. Each tile explains one result.
cm and in.
m².
At landing.
Shape.
Size.
Halving the landing speed needs four times the area, twice the diameter.
Frequently Asked Questions
No question matches that search.
How big a parachute do I need?
Work out the area from twice the weight divided by air density, drag coefficient and the speed squared, then convert to a diameter.
What landing speed is safe for a model rocket?
About three and a half to four and a half metres a second.
What is the drag coefficient of a parachute?
About one and a half for a dome and about zero point eight for a flat round canopy.
Why does doubling the size not halve the speed?
Speed falls with the square root of area, so you need four times the area to halve it.
Does altitude change parachute size?
Yes. Thinner air needs a bigger canopy for the same speed.
What is a spill hole?
A small hole at the top that lets air escape, steadying the canopy.
Can I use a plastic bag as a parachute?
For light models, yes, cut into a flat round or hexagon shape.
A soft landing every time
Size the canopy for the mass and the speed you want, and your rocket or payload lands ready to fly again.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.