# V-Belt Length and Center Distance Calculator

> Source: https://netray.co/tools/v-belt-length-and-center-distance-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Find the belt pitch length for two pulleys, the small-pulley wrap angle and belt speed, then back-solve the real center distance once you pick a standard belt length.

## Category

engineering-plm

## Industry

Industrial Machinery

## Audience

- Maintenance engineer
- Design engineer
- Plant engineer

## Tool

**Kind:** calculator

**Inputs:**

#### Small pulley pitch diameter

**Key:** d_small

**Type:** number

**Default:** 150

**Min:** 10

**Step:** 5

**Unit:** mm

**Help:** Pitch diameter, not outside diameter. For V-belts it is measured at the belt pitch line.

#### Large pulley pitch diameter

**Key:** d_large

**Type:** number

**Default:** 300

**Min:** 10

**Step:** 5

**Unit:** mm

#### Target center distance

**Key:** c_dist

**Type:** number

**Default:** 600

**Min:** 50

**Step:** 10

**Unit:** mm

#### Small pulley speed

**Key:** rpm_small

**Type:** number

**Default:** 1450

**Min:** 1

**Step:** 10

**Unit:** rpm

#### Standard belt pitch length chosen

**Key:** l_std

**Type:** number

**Default:** 1800

**Min:** 100

**Step:** 10

**Unit:** mm

**Help:** Enter the catalog pitch length you select after seeing the calculated length.

**Outputs:**

#### Belt pitch length at target center distance (mm)

**Key:** belt_len

**Expr:** 2 * c_dist + (pi / 2) * (d_large + d_small) + pow(d_large - d_small, 2) / (4 * c_dist)

**Format:** decimal

**Primary:** true

**Description:** L = 2C + 1.57 (D + d) + (D - d)^2 / 4C.

#### Small pulley wrap angle (degrees)

**Key:** wrap

**Expr:** 180 - 57.3 * (d_large - d_small) / c_dist

**Format:** decimal

**Description:** Below about 120 degrees, V-belt capacity falls quickly.

#### Belt speed (m/s)

**Key:** belt_speed

**Expr:** pi * d_small * rpm_small / 60000

**Format:** decimal

**Description:** Most V-belt drives run between 5 and 25 m/s.

#### Speed ratio

**Key:** speed_ratio

**Expr:** d_large / d_small

**Format:** decimal

#### Driven pulley speed (rpm)

**Key:** rpm_large

**Expr:** rpm_small / speed_ratio

**Format:** decimal

#### Intermediate term B

**Key:** b_term

**Expr:** 4 * l_std - 2 * pi * (d_large + d_small)

**Format:** decimal

#### Actual center distance for the standard belt (mm)

**Key:** c_actual

**Expr:** (b_term + sqrt(max(0, b_term * b_term - 32 * pow(d_large - d_small, 2)))) / 16

**Format:** decimal

**Primary:** true

**Description:** C = (B + sqrt(B^2 - 32 (D - d)^2)) / 16 where B = 4L - 6.28 (D + d).

#### Wrap angle at actual center distance (degrees)

**Key:** wrap_actual

**Expr:** 180 - 57.3 * (d_large - d_small) / c_actual

**Format:** decimal

**Chart:**

#### Belt length vs center distance

**Type:** line

**X:** c_dist

**From:** 300

**To:** 1500

**Steps:** 25

**Series:**

- belt_len

**Disclaimer:** Open-belt geometry using pitch diameters. Belt power rating, service factor and number of belts must come from the belt manufacturer's catalog.

## Content

**Intro:** This calculator gives the pitch length of an open belt around two pulleys and then does the reverse calculation: the true center distance you get when you fit the nearest standard belt. Maintenance and design engineers use it to order replacement belts and to set motor base travel.

**Sections:**

#### How to use the calculator

**Body:** Enter the pitch diameters of both pulleys, the center distance you would like, and the speed of the small pulley. The calculator returns the exact belt length needed, the wrap angle on the small pulley, the belt speed and the driven speed. Pick the nearest standard belt pitch length from a catalog, type it into the standard length field and read the actual center distance. Make sure the motor base can move at least a few percent either side for tensioning and installation.

#### Formulas used

**Body:** For an open belt drive the length is L = 2C + (pi / 2)(D + d) + (D - d)^2 / (4C), with D and d the large and small pitch diameters and C the center distance. The small pulley wrap angle is approximately 180 minus 57.3 (D - d) / C degrees. Solving for C given a standard length uses C = (B + sqrt(B^2 - 32 (D - d)^2)) / 16 with B = 4L - 2 pi (D + d). Belt speed is pi x d x rpm / 60000 in meters per second.

#### Interpreting results

**Body:** Using the defaults, the belt is about 1,916 mm long and wraps about 166 degrees on the small pulley. If you choose an 1,800 mm belt, the center distance becomes about 541 mm, a 59 mm change that the motor slide must absorb. A wrap angle under 120 degrees means the drive is slipping risk territory, so increase center distance or add an idler. Speed above 25 m/s on a classical V-belt calls for narrow section or banded belts.

#### Common mistakes

**Body:** People often use pulley outside diameter instead of pitch diameter, which makes the belt too long. Others forget that a shorter standard belt increases the speed ratio of wrap loss, or that the belt must be installed with the center distance reduced, then tensioned. Timing belts follow tooth pitch rules instead, so their length must be a whole number of teeth. Check your catalog length basis (pitch, inside or outside) before ordering.

**Cta:** If belt, chain and spare part data sits in separate spreadsheets, Netray can help map it into your maintenance and inventory modules.

**Faq:**

#### How do I calculate belt length for two pulleys?

**Answer:** Use L = 2C + 1.57 x (D + d) + (D - d)^2 / (4C) with pitch diameters and center distance in the same unit. Then round to the nearest standard belt length and recalculate the actual center distance so the motor base can reach it.

#### What is a good wrap angle for a V-belt drive?

**Answer:** Aim for 120 degrees or more on the small pulley. Below that the belt grips poorly and manufacturers apply an arc-of-contact correction that cuts the power rating. Increasing center distance or reducing the speed ratio raises the wrap angle.

#### Is belt length measured at the pitch line?

**Answer:** For most V-belts catalogs use pitch length, which is measured on the neutral axis of the belt. Some list inside or outside length, so confirm the basis for the belt series. Pulley diameters in the formula must also be pitch diameters.

#### How much center distance adjustment do I need?

**Answer:** Typical guidance is to allow about 1.5 percent of belt length for tightening and about 3 percent for installation without forcing the belt over the flange, but belt makers publish exact figures by section. Check the catalog for your belt series.

## Search terms

v belt length calculator, belt center distance calculator, belt length formula two pulleys, pulley center distance calculator, belt drive calculator, belt wrap angle calculator, belt speed calculator, pulley ratio calculator

---
Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json