Pulley Ratio Calculator
The Pulley Ratio Calculator determines speed and torque relationships between driver and driven pulleys. Enter pulley diameters to find the speed ratio, output RPM, and torque multiplication for belt-driven machinery, HVAC systems, and industrial equipment.
What is a Pulley Ratio?
A pulley ratio is the relationship between the diameters (or number of grooves) of two pulleys connected by a belt. When a small pulley drives a larger one, the output speed decreases but torque increases. A 4-inch driver pulley turning a 12-inch driven pulley creates a 3:1 ratio — speed is reduced by 3× and torque is multiplied by 3×.
Pulley ratios are used in industrial machinery, automotive accessory drives, HVAC blower systems, drill presses, and exercise equipment. Variable-speed pulleys allow infinite ratio adjustment by changing the effective diameter.
Formula & Persamaan Yang Digunakan
Pulley Ratio Calculator ini menggunakan 5 persamaan utama:
1 Pulley Speed Ratio ▼
6-inch driver and 12-inch driven: Ratio = 6/12 = 1:2 (speed halved, torque doubled).
2 Output RPM ▼
Motor at 1750 RPM with 3" driver and 9" driven: Output = 1750 × (3/9) = 583 RPM.
3 Torque Output ▼
10 ft-lb input with 2:1 ratio: Output = 10 × 2 = 20 ft-lb (minus belt losses).
Cara Menggunakan Kalkulator Ini
Untuk menggunakan Kalkulator Nisbah ini, ikuti 3 langkah berikut:
Masukkan Nilai
Taip nilai nisbah yang diketahui ke dalam ruang input. Biarkan satu ruang kosong — itu ialah nilai tidak diketahui yang diselesaikan oleh Kalkulator Nisbah.
Pilih Mod
Pilih mod nisbah — Selesaikan, Permudahkan, atau Skalakan. Setiap mod menggunakan persamaan berbeza untuk nilai input anda.
Dapatkan Hasil
Klik Kira. Skrin hasil memaparkan jawapan dengan bar nisbah visual, carta pai, dan pecahan jalan pengiraan langkah-demi-langkah.
Contoh Masalah & Penyelesaian Langkah-demi-Langkah
Berikut ialah 3 contoh masalah dengan penyelesaian langkah-demi-langkah menggunakan Kalkulator Nisbah ini:
Input 1 Motor: 1750 RPM, 4" driver, 10" driven pulley
Input 2 Find driver pulley size for 500 RPM output from 1200 RPM motor
Input 3 Two-stage pulley system: 3:1 then 2:1
Soalan Lazim
How does pulley size affect speed? ▼
A larger driven pulley reduces output speed but increases torque. A smaller driven pulley increases speed but reduces torque. The ratio is directly proportional to the diameter ratio of the two pulleys.
Do V-belts slip and affect the ratio? ▼
Well-tensioned V-belts have minimal slip (1-3%). For precise applications, use timing belts (cogged/synchronous belts) which have zero slip and maintain exact speed ratios.
Can I use different sized pulleys to save energy? ▼
Matching pulley ratios to the required load speed improves efficiency. Running a fan at 75% speed (using pulley ratio) reduces power consumption by about 58% due to the fan affinity laws (power ∝ speed³).
What is a variable speed pulley? ▼
A variable speed pulley (VP) has adjustable halves that change the effective diameter. As the halves spread apart, the belt rides lower, changing the ratio. This allows continuous speed adjustment without changing pulleys.
How do I calculate belt length for two pulleys? ▼
Belt Length ≈ 2C + π(D+d)/2 + (D-d)²/(4C), where C = center distance, D = large pulley diameter, d = small pulley diameter. Add 1-2% for tensioning.