When dealing with small engines—such as those in motorcycles, lawn mowers, or generators—it’s useful to understand the relationship between horsepower (HP) and cubic centimeters (CC).
This tool calculates CC value from HP
Enter the value of Horsepower (HP), the conversion factor (15 to 17) and the tool will provide the equivalent CC value.
Formula
Here’s a simple formula to estimate the CC from HP:
CC ≈ HP × 15 to 17
This formula provides a ballpark estimate. For a more accurate calculation, it’s best to consider the engine type and manufacturer specifications.
Example Conversions
- 5 HP Engine:
5 × 15 = 75 CC (low estimate)
5 × 17 = 85 CC (high estimate) - 10 HP Engine:
10 × 15 = 150 CC
10 × 17 = 170 CC
These estimates are helpful when comparing engines, but actual performance may vary depending on engine design.
Background
While HP measures the power output, CC measures the engine’s displacement (size). However, converting between these units isn’t straightforward, as engine design and efficiency affect the relationship. In this article, we’ll explain how to estimate HP to CC conversion, explore key factors to consider, and introduce tools that help with this calculation.
What Are HP and CC?
- Horsepower (HP): A measurement of power output. One horsepower equals the force required to move 550 pounds one foot in one second. In small engines, more HP generally means more power for tasks like mowing thick grass or powering vehicles.
- Cubic centimeters (CC): A measurement of the engine’s displacement—how much air and fuel the engine can draw in during one full cycle. A higher CC generally indicates a larger engine capable of producing more power.
The Relationship Between HP and CC
There is no precise conversion formula from HP to CC because the power an engine produces depends on several factors:
- Engine efficiency
- Compression ratio
- Fuel type
- Engine type (two-stroke or four-stroke)
However, as a rough estimate, most small engines have a power ratio of:
1 HP ≈ 15 to 17 CC
This means that, for an average engine, you can assume around 15 to 17 cubic centimeters of engine displacement per horsepower.
Quick HP to CC Conversion Table (Approximate)
| Horsepower (HP) | Engine Size (CC) |
|---|---|
| 3 HP | 45 to 51 CC |
| 5 HP | 75 to 85 CC |
| 8 HP | 120 to 136 CC |
| 10 HP | 150 to 170 CC |
| 12 HP | 180 to 204 CC |
| 15 HP | 225 to 255 CC |
Factors That Affect HP to CC Conversion
Two-Stroke vs. Four-Stroke Engines
- Two-stroke engines: Produce more power per CC but are less fuel-efficient.
- Four-stroke engines: Produce less power per CC but are quieter, more fuel-efficient, and have a longer lifespan.
Engine Efficiency
More efficient engines can generate higher HP with fewer CC. Factors like the compression ratio and fuel delivery system (e.g., carburetor vs. fuel injection) can impact power output.
Fuel Type
Engines running on different fuels—such as gasoline, ethanol blends, or diesel—can produce varying power outputs, even with the same engine size.
Using an HP to CC Calculator
To make conversions easy, you can use an online HP to CC calculator. These calculators help estimate the engine size based on the given horsepower. Simply enter the HP, and the tool will return the approximate CC value based on the 15 to 17 CC per HP ratio.
How to Use an HP to CC Calculator:
- Enter the HP value (e.g., 6 HP).
- Select the engine type (two-stroke or four-stroke, if applicable).
- Click “Calculate” to get the estimated CC value.
- Use the result to compare engine sizes or choose the right engine for your needs.
When You Might Need HP to CC Conversion
- Buying Equipment: Compare power ratings for lawn mowers, go-karts, or generators.
- Modifying Engines: Choose the right size for upgrades or tuning.
- Estimating Performance: Get a rough idea of an engine’s size when only the HP is known.
- Rental or Repair Services: Find replacement engines with similar power output.
Limitations of HP to CC Calculations
While the 15 to 17 CC per HP ratio provides a useful estimate, it’s important to understand that no formula can perfectly predict the actual engine size or performance.
Always check the manufacturer’s specifications for the most accurate measurements.
Two engines with the same CC rating might have very different HP outputs due to differences in fuel systems, engine tuning, and efficiency. When precision matters, refer to official engine manuals or product labels.
Summary
An HP to CC conversion gives you a practical way to estimate the size of an engine based on its horsepower. While no exact formula exists, using a 15 to 17 CC per HP ratio offers a reasonable approximation.
For more accurate results, consider factors like engine type (two-stroke or four-stroke), fuel type, and efficiency. When available, always refer to the manufacturer’s specifications for precise measurements.
And if you want to save time, use the calculator on this page to make quick estimates.