Engines for model rockets are classified based on the total impulse of the rocket engine. Classes A through G are for model rocketry, while classes H through O are for high power rocketry and require special certification and licensing.
| Classification | Impulse | Skill Levels | Typical Uses |
| 1/2A-class | .63-1.25 Newton-seconds | Skill Level 1 | kits, starter sets, launch sets |
| A-class | 1.26-2.50 Newton-seconds | Skill Level 1 | kits, starter sets, launch sets |
| B-class | 2.51-5.00 Newton-seconds | Skill Level 1 & 2 | kits, starter sets, launch sets |
| C-class | 5.01-10.00 Newton-seconds | Skill Level 1 & 2 & 3 | kits, starter sets |
| D-class | 10.01-20.00 Newton-seconds | Skill Level 2 & 3 | model rocket kits |
| E-class | 20.01-40.00 Newton-seconds | Skill Level 3 & 4 | model rocket kits |
| F-class | 40.01-80.00 Newton-seconds | Skill Level 4 | model rocket kits |
| G-class | 80.01-160.00 Newton-seconds | Skill Level 4 | model rocket kits |
1/2A-class
An 1/2A-class model rocket engine is a single-use engine designed to launch a model rocket. 1/2A-class rocket engines typically have the following properties:
- Total Impulse of .63-1.25 Newton-seconds
- Length of 2 3/4"
- Diameter of 1/2" (to fit inside a BT-5 rocket, or engine mount kit) (exceptions are the mini-engines)
A-class
An A-class model rocket engine is a single-use engine designed to launch a model rocket. A-class rocket engines have the following properties:
- Total Impulse of 1.26-2.50 Newton-seconds
- Length of 2 3/4"
- Diameter of 1/2" (to fit inside a BT-5 rocket, or engine mount kit)
B-class
An B-class model rocket engine is a single-use engine designed to launch a model rocket. B-class rocket engines have the following properties:
- Total Impulse of 2.51-5.00 Newton-seconds
- Length of 2 3/4"
- Diameter of 1/2" (to fit inside a BT-5 rocket, or engine mount kit)
C-class
An C-class model rocket engine is a single-use engine designed to launch a model rocket. C-class rocket engines have the following properties:
- Total Impulse of 5.01-10.00 Newton-seconds
- Length of 2 3/4"
- Diameter of 1/2" (to fit inside a BT-5 rocket, or engine mount kit). Exception - the Estes C11-3 and C11-7 have a diameter of 1"
D-class
The D-class model rocket engine is for launching fairly large model rockets, and these engines come in two different variations.
- The most popular is the Estes D-class single-use engines, which are designed to be used in Estes model rockets.
- Aerotech reloadable model rocket engine.
E-class
The E-class model rocket engine is for launching fairly large model rockets, and these engines come in two different variations. This is the largest that black-powder based model rocket engines can be safely manufactured.
- The most popular is the Estes E-class single-use engines, which are designed to be used in Estes model rockets.
- Aerotech reloadable model rocket engine.
F-class
The F-class model rocket engine is for launching fairly large model rockets, and these engines come in two different variations. This is the largest that black-powder based model rocket engines can be safely manufactured.
- Aerotech single-use model rocket engine.
- Aerotech reloadable model rocket engine.
G-class
The G-class model rocket engine is for launching fairly large model rockets, and these engines come in two different variations. This is the largest that black-powder based model rocket engines can be safely manufactured.
- Aerotech single-use model rocket engine.
- Aerotech reloadable model rocket engine.