When to use this calculator
Estimate the pitch length of an open two-pulley belt. Common open-belt approximation; standard belt selection and tension allowances are separate.
Explore the gears, belts & motion calculators for other questions in this topic. For a related calculation, use the Cutting Speed Calculator: Find surface cutting speed from tool diameter and rotational speed.
PUTTING IT INTO PRACTICE
Open Belt Length: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Larger pitch diameter (mm) | 200 |
| Smaller pitch diameter (mm) | 100 |
| Centre distance (mm) | 500 |
| Result | 1,476.238898 mm |
- Check the input labels and enter the example values above.
- Apply the relationship: Approximate length = 2C + π(D+d)/2 + (D−d)²/(4C).
- The result is 1,476.238898 mm, rounded for display.
How to interpret your result
Common open-belt approximation; standard belt selection and tension allowances are separate.
Use compatible modules and effective pitch dimensions. No-slip and ideal-mesh assumptions omit losses and dynamics. A ratio calculation does not select a safe shaft, belt, bearing or gear rating.
Frequently asked questions
Why is a lead-screw lead different from its pitch?
Pitch is the axial distance between thread forms. A multi-start screw advances by pitch times the number of starts per revolution.
When is the open belt length calculator useful?
Estimate the pitch length of an open two-pulley belt. Common open-belt approximation; standard belt selection and tension allowances are separate.
How do I use the open belt length calculator?
Enter larger pitch diameter (mm), smaller pitch diameter (mm), centre distance (mm). The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Approximate length = 2C + π(D+d)/2 + (D−d)²/(4C).
What should I check before using the result?
Common open-belt approximation; standard belt selection and tension allowances are separate.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
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