Engineering reference – source controlled

V-Belt Catalog Rating and Geometry Calculator

For an open, two-pulley reduction drive with the smaller pulley driving. The tool calculates geometry and applies power ratings only when you enter the exact values from one identified manufacturer catalog.

ISO scope correctedNo invented power tableExplicit calculation

Do not use the old result. ISO 4184:2025 specifies requirements for classical and narrow V-belts and their datum-length system; it is not a universal belt-power selection table. ISO 5288:2024 is vocabulary for synchronous belt drives and is not applicable to this V-belt calculation. Final profile, pulley, length, tension, shaft load, guarding and environmental suitability must be verified in the current manufacturer procedure.

Calculation record

All fields are required. Decimal point and decimal comma are accepted; grouped numbers and unit suffixes are rejected.

Enota moči

Diameter and centre-distance unit

Transmitted power, P Rated or otherwise defined power required by the chosen catalog method.

Catalog service/load factor, c2 Copy from the same manufacturer method; do not infer it from a generic machine label.

Small driver pulley speed, n1 (rpm)

Small driver datum diameter, d1 Use datum diameter, not outside diameter.

Large driven datum diameter, d2

Shaft centre distance, a

Catalog nominal power per belt, PN For the exact profile, datum diameter, speed, ratio, belt family and catalog basis.

Catalog arc-of-contact factor, c1 Must be greater than 0 and no greater than 1 for this restricted method.

Catalog belt-length factor, c3

Exact rating source record

Required confirmations I copied PN, c1, c2 and c3 from the same identified manufacturer method and matched its belt family, profile, diameter, speed, ratio, length and units. This is an open two-pulley reduction drive; d1 is the smaller driving datum diameter, d2 is the larger driven datum diameter, and a is the shaft centre distance. I will verify the selected standard/catalog length, minimum pulley diameter, permissible belt speed, tension, shaft loads, matched set, environment, dynamic balance, alignment, guarding and final engineering approval.

Preliminary belt quantity

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The raw calculated ratio is rounded upward; this is not final drive approval.

Calculated belt ratio, zth

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Design power, PB

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Corrected capacity per belt

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Nominal ratio / driven speed

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Belt speed

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Kot ovoja na mali jermenici

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Theoretical datum length

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Rating source entered:

Stop before procurement or operation. The result does not select an ISO/catalog belt length, verify a pulley profile, calculate installation tension, confirm shaft or bearing loads, assess torsional dynamics, or establish guarding and lockout procedures. Complete the manufacturer’s design process and an engineering review.

Formulas and scope

These equations are the open-belt geometry and catalog-rating workflow shown in the official Optibelt technical manual. They are not described here as formulas from ISO 4184.

Catalog rating

PB = P * c2

Pcorrected = PN * c1 * c3

zth = PB / Pcorrected ; z = ceil(zth)

PN and the factors are product- and manufacturer-specific. Mixing values from different catalogs or belt families invalidates the result.

Ratio, speed and open-belt geometry

i = d2 / d1 ; n2 = n1 / i

v = pi * d1 * n1 / 60000 [d1 in mm, n1 in rpm, v in m/s]

alpha = asin((d2 – d1) / (2a)) ; beta = pi – 2alpha

Ld = 2a*cos(alpha) + (pi/2)(d1 + d2) + alpha(d2 – d1)

Ld,approx = 2a + (pi/2)(d1 + d2) + (d2 – d1)^2 / (4a)

Diameters and centre distance must use one consistent length unit; the calculator converts to millimetres. The theoretical datum length must be replaced by an available standard/catalog length and the final centre distance must then be recalculated in the manufacturer’s procedure.

Standardi in meja virov

On a small screen, scroll the source table horizontally.

Vir	Status checked 16 July 2026	What it supports here	What it does not support here
ISO 4184:2025, Edition 3	Published, October 2025; replaces ISO 4184:1992	Requirements for classical sections Y-Z-A-B-C-D-E and narrow sections SPZ-SPA-SPB-SPC; datum-length system.	No universal service factor, belt power rating, profile recommendation or belt-count table is inferred from its public record.
ISO 4183:2026, Edition 4	Published, January 2026; replaces ISO 4183:1995	Principal pulley-groove dimensions in the datum-width system.	Not a universal drive power-rating method.
ISO 1081:2013, Edition 3	Published but marked “to be revised”; ISO/DIS 1081 under development	Vocabulary and the distinction between datum-width and effective-width systems.	Does not make values from the two systems interchangeable.
ISO 5288:2024, Edition 4	Published, November 2024	Synchronous-belt vocabulary only.	Not applicable as the selection standard for this friction V-belt drive.
Optibelt Technical Manual – V-Belt Drives	Official manufacturer PDF retrieved 16 July 2026; PDF metadata modified 22 January 2024	Pages 72 and 83-85 show the catalog factors, geometry, published example and z = Pc2/(PNc1*c3).	Its ratings and factors must not be presented as universal values for other manufacturers.

NEEDS_LICENSED_SOURCE: the exact ISO 4184:2025 standard datum-length series, tolerances and measurement conditions are not reproduced. Use a licensed copy and the applicable manufacturer catalog before selecting a purchasable belt.

Published example check

Optibelt’s pages 83-85 use P = 132 kW, c2 = 1.3, d1 = 280 mm, d2 = 500 mm, n1 = 1485 rpm, a = 1383.5 mm, PN = 21.87 kW/belt, c1 = 1.00 and c3 = 1.02. The published belt-count ratio is 7.69 and the recommendation is eight SPB belts for that identified example. Using unrounded inputs here gives zth = 7.692515, belt speed 21.771 m/s and a theoretical datum length about 4000.972 mm. The example button loads these values but deliberately does not check the required confirmations.

Questions and limitations

Why is there no automatic profile recommendation?

A power range alone is insufficient. Profile selection depends on the manufacturer’s rating chart or software, speed, pulley diameter, ratio, belt length, duty, environment and product family. The old generic ranges had no controlled source.

Why must all catalog factors come from one source?

The nominal power rating is established under stated reference conditions. Arc, length and service factors correct that specific basis. Combining unrelated tables can double-count or omit corrections.

Does the calculated quantity approve the drive?

No. It is only the upward-rounded catalog capacity ratio after the entered factors. Final selection still requires the complete manufacturer procedure, tension and shaft-load checks, standard/catalog length selection, dynamics and safety review.

Can I use outside pulley diameters?

No. This restricted calculator requires datum diameters. ISO 1081 distinguishes datum-width and effective-width systems; outside, datum and effective diameters are not interchangeable without the applicable product data.