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Calcimator

Model Rocket Motor Calculator

Determine the right motor class for your model rocket based on weight, target altitude, body diameter, and drag.

Inputs

Results

Required Impulse (Ns)

85

Motor Class (1=A, 7=G+)

7

Thrust-to-Weight Ratio38.5
Estimated Altitude (ft)500
Typical Burn Time (sec)1.5
How to Use This Calculator
  1. Enter Rocket Weight (grams), Target Altitude (feet), and Body Diameter (mm).
  2. Set Drag Coefficient.
  3. Review Required Impulse (Ns) and Motor Class (1=A, 7=G+).
  4. Use Thrust-to-Weight Ratio and Estimated Altitude (ft) to inform your decision.
  5. Use the chart to visualize the results and explore different scenarios by adjusting inputs.

How the result changes with Rocket Weight (grams)

Rocket Weight (grams)Required Impulse (Ns)Motor Class (1=A, 7=G+)
5092887
1,7579957
3,2541,8437
4,5012,5507

What each input means

Rocket Weight (grams)
Total ready-to-fly weight without motor (airframe, recovery, payload)
Target Altitude (feet)
Desired maximum altitude in feet
Body Diameter (mm)
Rocket body tube outer diameter in millimeters
Drag Coefficient
Aerodynamic drag coefficient (0.3-0.5 for sleek rockets, 0.6-0.8 for blunt)

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Rocket Weight (grams) = 150, Target Altitude (feet) = 500, Body Diameter (mm) = 25, Drag Coefficient = 0.5 = 4 input(s) provided
  2. Calculate Required Impulse
    Required Impulse
    85 = 85
  3. Calculate Motor Class
    7 = 7
  4. Calculate Thrust-to-Weight Ratio
    Thrust-to-Weight Ratio
    38.5 = 38.5
  5. Calculate Estimated Altitude
    Estimated Altitude
    500 = 500

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