How do I select the right V-belt cross-section?

V-belt cross-section is selected based on design power (power × service factor) and the speed of the faster shaft. Use selection charts: Z/SPZ for up to ~4 kW, A/SPA for ~2-20 kW, B/SPB for ~5-60 kW, C/SPC for ~15-150 kW, D for ~50-500 kW.

What is the difference between classical and narrow V-belts?

Classical V-belts (Z, A, B, C, D) have a wider profile. Narrow V-belts (SPZ, SPA, SPB, SPC) transmit more power per belt and per unit width. Narrow belts are preferred for new designs due to higher power density and efficiency.

How do I calculate the number of belts needed?

Number of belts = Design Power / (Power per belt × Correction factors). Correction factors include wrap angle factor (C1), belt length factor (C3), and number-of-belts factor. Round up to the nearest whole number.

What service factors apply to V-belt drives?

Service factors for V-belts: 1.0-1.2 for uniform loads (fans, pumps), 1.1-1.3 for light shocks, 1.2-1.4 for moderate shocks, 1.3-1.8 for heavy shocks. Multiply by 1.2 for more than 10 hours/day operation.

What is the maximum recommended V-belt speed?

Maximum recommended belt speed: 25-30 m/s for classical V-belts, up to 40 m/s for narrow V-belts. Above these speeds, centrifugal forces significantly reduce belt capacity and special high-speed belts should be used.

Free Engineering Tool #088

V-Belt Selection Calculator

Select V-belt cross-section and calculate the number of belts needed per ISO 5288. Enter power, speed, service factor, and pulley diameter.

ISO 5288 Z/A/B/C/D SPZ/SPA/SPB/SPC

Power (kW)

Faster Shaft Speed (RPM)

Service Factor

Small Pulley Diameter (mm)

Belt Profile

Speed Ratio (D₂/D₁)

Quick presets

Results

Number of Belts Required

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Design Power (P_d)

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Power Per Belt (P_b)

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Recommended Profile

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Belt Speed

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Design Power

Number of Belts

Where C₁ is wrap angle factor, C₃ is belt length factor, and P_b is the basic power rating per belt.

V-Belt Cross-Section Selection Guide

Profile	Type	Top Width	Power Range (typical)	Min Pulley ⌀
Z	Classical	10 mm	0.2 – 4 kW	50 mm
A	Classical	13 mm	0.5 – 15 kW	75 mm
B	Classical	17 mm	2 – 55 kW	125 mm
C	Classical	22 mm	10 – 150 kW	200 mm
D	Classical	32 mm	40 – 500 kW	355 mm
SPZ	Narrow	9.7 mm	0.5 – 8 kW	63 mm
SPA	Narrow	12.7 mm	1.5 – 30 kW	90 mm
SPB	Narrow	16.3 mm	5 – 80 kW	140 mm
SPC	Narrow	22 mm	20 – 250 kW	224 mm

Tip: Narrow V-belts (SPZ, SPA, SPB, SPC) offer 30–50% more power capacity per belt than classical sections and are recommended for new designs.

V-Belt Selection Calculator | ISO 5288 | Free Online Tool

Published by Nikolai Shelkovenko on February 15, 2026 February 15, 2026

Results

Design Power

Number of Belts

V-Belt Cross-Section Selection Guide