This free Motor Belt Pulley Bearing Calculator gives HVAC technicians instant belt length, pulley ratio, fan RPM, and bearing-size results, right in the browser โ no sign-up, no app download.
Motor, Belt, Pulley and Bearing Calculator
Get the right belt size, pulley ratio and bearing number instantly. No sign-up and no app download, just calculate in your browser.
| Bearing No. | Series | Bore (mm) | OD (mm) | Width (mm) |
|---|
| Motor HP | Typical Pulley Size Range | Typical Belt Type | Typical Bearing Size |
|---|
Belt Tension Check (Deflection Method)
Press lightly by hand at the middle of the belt span and check the deflection. Standard rule: about 1/64 inch (0.4mm) of deflection for every 1 inch (25.4mm) of span length is normal.
Bearing Numbering System
Example: 6 2 05 โ pehla digit series type (6 = deep groove ball bearing), doosra digit dimension series (0/2/3 = light/medium load), aakhri do digits bore code (ร 5 = bore in mm; 00=10, 01=12, 02=15, 03=17mm).
Table of Contents
How This Motor Belt Pulley Bearing Calculator Works
This Motor Belt Pulley Bearing Calculator helps HVAC technicians quickly work out drive-system numbers on the job: pulley ratio, driven-shaft RPM, belt length, and bearing size. These are the same calculations used when replacing a blower motor, resizing a pulley, or troubleshooting an AHU or cooling-tower fan that isn’t turning at the right speed.
For the underlying bearing-life (L10) standard used by manufacturers, see ISO 281 โ Rolling Bearings Life Rating. Getting pulley ratios right matters especially in Gulf-region HVAC work, where AHU and cooling-tower fans run long hours in high ambient heat โ an incorrect ratio means the motor works harder than it should, shortening bearing and belt life.
Motor Belt Pulley Bearing Formulas With Examples
The calculator above uses these standard formulas, so you can check any result by hand.
| Calculation | Formula | Example |
|---|---|---|
| Open belt length | L = 2C + (ฯ/2)(D + d) + (D โ d)ยฒ รท 4C | D = 120 mm, d = 180 mm, C = 500 mm gives L = 1473.04 mm (57.99 in) |
| Fan RPM | Fan RPM = Motor RPM ร (Motor pulley รท Fan pulley) | 1440 ร (120 รท 180) = 960 RPM |
| Pulley ratio | Fan pulley รท Motor pulley | 180 รท 120 = 1.5 (a 1 : 1.5 speed-reduction drive) |
| Bearing size from shaft | Match shaft diameter to the standard bore | 25 mm shaft: 6005, 6205 or 6305 bearing |
In the belt length formula, C is the center distance between the two shafts, D is the motor pulley diameter and d is the fan pulley diameter, all in the same unit. The result is the calculated belt length, so choose the nearest standard belt size. Fan RPM comes from equal belt speed at both pulleys, so a larger fan pulley always runs slower than the motor.
The bearing tabs are lookups for the 6000, 6200 and 6300 series (10 to 75 mm bore). They show bore, outer diameter and width, for example 6205 is 25 mm bore, 52 mm OD and 15 mm wide. They do not calculate bearing life.
Frequently Asked Questions
How do I calculate pulley ratio for a motor?
Divide the driven pulley diameter by the driver (motor) pulley diameter. This Motor Belt Pulley Bearing Calculator does this instantly and also gives you the resulting driven RPM.
How do I estimate bearing life?
Bearing life (L10) is estimated using the dynamic load rating (C) divided by the actual load (P), cubed, multiplied by one million revolutions. For example, C = 20 kN and P = 4 kN gives (20 รท 4)ยณ = 125 million revolutions, or about 1,447 hours at 1440 RPM. This calculator finds bearing sizes only; use the bearing maker’s datasheet for C and P.
Why does correct pulley sizing matter for HVAC motors?
Wrong pulley ratios push the motor and bearings to run outside their design speed, causing premature belt wear, excess vibration, and shortened motor and bearing life โ especially in continuously-running Gulf-climate HVAC systems.
How do I calculate V-belt length?
Use L = 2C + (ฯ/2)(D + d) + (D โ d)ยฒ รท 4C, where C is the center distance and D and d are the pulley diameters. With D = 120 mm, d = 180 mm and C = 500 mm, the belt length is 1473.04 mm (57.99 in). Pick the nearest standard belt size.
How do I find fan RPM from pulley sizes?
Fan RPM = Motor RPM ร (Motor pulley diameter รท Fan pulley diameter). A 1440 RPM motor with a 120 mm motor pulley and a 180 mm fan pulley turns the fan at 960 RPM.
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