Machining Speeds & Feeds Card
One page. Speeds, chip load and drill feed, imperial and metric.
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BuyPulley / Sheave Size Chart
Common shop diameters with speed ratios at 1725 and 3450 RPM motors
This chart is a planning reference for open V-belt drives using diameter ratio. It assumes negligible slip and uses outside/pitch diameter interchangeably as a shop approximation — for critical compressor or spindle limits, prefer catalog pitch diameter and verify with a tachometer.
Non-standard size?Any diameters, reverse sizing, and belt length.
Open Calculator →How to Read This Chart
Each row pairs a driver (motor) pulley diameter with a driven pulley diameter. Ratio is driven÷driver. RPM @ 1725 and RPM @ 3450 are the driven-shaft speeds for those common single-phase motor nameplates using N₂ = N₁ × (D₁ / D₂).
Use the chart when you are standing in front of a shelf of cast sheaves and need a fast shortlist. Then confirm center distance, belt section, and horsepower rating before you buy. The interactive tool is better when one diameter is already fixed and you are solving for the other — that is reverse mode on the Pulley & Belt Ratio Calculator.
Motor RPM is not always 1725 or 3450. Read the nameplate. Soft-start VFDs, three-phase frames, and generator-duty motors differ. Wrong N₁ makes every chart cell wrong.
Why These Diameters
The diameters listed — roughly 2" through 12" — cover the majority of fractional-horsepower to ~5 HP shop drives: drill-press steps, compressor motor/pump sheaves, bench-lathe countershafts, and buffer/grinder conversions. Below ~2" on classical V-belts, bend stress climbs and belt life falls; above ~12" on small frames you often run out of guard clearance or center-distance adjustment.
Skipping identical driver/driven pairs keeps the table focused on actual ratio changes. A 1:1 pair is still valid mechanically (idler-like speed match) but it is rarely the answer when you opened a chart to change speed.
Common Shop Size Reference
| Driver (in) | Driven (in) | Ratio D₂/D₁ | RPM @ 1725 | RPM @ 3450 |
|---|---|---|---|---|
| 2.0 | 2.5 | 1.250:1 | 1380 | 2760 |
| 2.0 | 3.0 | 1.500:1 | 1150 | 2300 |
| 2.0 | 4.0 | 2.000:1 | 862 | 1725 |
| 2.0 | 5.0 | 2.500:1 | 690 | 1380 |
| 2.0 | 6.0 | 3.000:1 | 575 | 1150 |
| 2.0 | 8.0 | 4.000:1 | 431 | 862 |
| 2.0 | 10.0 | 5.000:1 | 345 | 690 |
| 2.0 | 12.0 | 6.000:1 | 288 | 575 |
| 2.5 | 3.0 | 1.200:1 | 1438 | 2875 |
| 2.5 | 4.0 | 1.600:1 | 1078 | 2156 |
| 2.5 | 5.0 | 2.000:1 | 862 | 1725 |
| 2.5 | 6.0 | 2.400:1 | 719 | 1438 |
| 2.5 | 8.0 | 3.200:1 | 539 | 1078 |
| 2.5 | 10.0 | 4.000:1 | 431 | 862 |
| 2.5 | 12.0 | 4.800:1 | 359 | 719 |
| 3.0 | 2.5 | 0.833:1 | 2070 | 4140 |
| 3.0 | 4.0 | 1.333:1 | 1294 | 2588 |
| 3.0 | 5.0 | 1.667:1 | 1035 | 2070 |
| 3.0 | 6.0 | 2.000:1 | 862 | 1725 |
| 3.0 | 8.0 | 2.667:1 | 647 | 1294 |
| 3.0 | 10.0 | 3.333:1 | 518 | 1035 |
| 3.0 | 12.0 | 4.000:1 | 431 | 862 |
| 3.5 | 2.5 | 0.714:1 | 2415 | 4830 |
| 3.5 | 3.0 | 0.857:1 | 2013 | 4025 |
| 3.5 | 4.0 | 1.143:1 | 1509 | 3019 |
| 3.5 | 5.0 | 1.429:1 | 1208 | 2415 |
| 3.5 | 6.0 | 1.714:1 | 1006 | 2013 |
| 3.5 | 8.0 | 2.286:1 | 755 | 1509 |
| 3.5 | 10.0 | 2.857:1 | 604 | 1208 |
| 3.5 | 12.0 | 3.429:1 | 503 | 1006 |
| 4.0 | 2.5 | 0.625:1 | 2760 | 5520 |
| 4.0 | 3.0 | 0.750:1 | 2300 | 4600 |
| 4.0 | 5.0 | 1.250:1 | 1380 | 2760 |
| 4.0 | 6.0 | 1.500:1 | 1150 | 2300 |
| 4.0 | 8.0 | 2.000:1 | 862 | 1725 |
| 4.0 | 10.0 | 2.500:1 | 690 | 1380 |
| 4.0 | 12.0 | 3.000:1 | 575 | 1150 |
| 5.0 | 2.5 | 0.500:1 | 3450 | 6900 |
| 5.0 | 3.0 | 0.600:1 | 2875 | 5750 |
| 5.0 | 4.0 | 0.800:1 | 2156 | 4312 |
| 5.0 | 6.0 | 1.200:1 | 1438 | 2875 |
| 5.0 | 8.0 | 1.600:1 | 1078 | 2156 |
| 5.0 | 10.0 | 2.000:1 | 862 | 1725 |
| 5.0 | 12.0 | 2.400:1 | 719 | 1438 |
| 6.0 | 2.5 | 0.417:1 | 4140 | 8280 |
| 6.0 | 3.0 | 0.500:1 | 3450 | 6900 |
| 6.0 | 4.0 | 0.667:1 | 2588 | 5175 |
| 6.0 | 5.0 | 0.833:1 | 2070 | 4140 |
| 6.0 | 8.0 | 1.333:1 | 1294 | 2588 |
| 6.0 | 10.0 | 1.667:1 | 1035 | 2070 |
| 6.0 | 12.0 | 2.000:1 | 862 | 1725 |
Values rounded to the nearest RPM. Recalculate with exact measured diameters for final setup.
Pitch Diameter, Slip, and Real Machines
Catalog sheaves publish pitch diameter for a reason: the belt’s tensile cord line does not sit at the outside rim. Using OD in this chart slightly misstates ratio — usually by a few percent on classical A/B sections, more on deep narrow profiles. If your compressor pump has a hard RPM ceiling, that few percent matters.
Slip under load lowers real RPM further. A glazed belt on a polished groove can give up several percent before you smell it. If tach readings disagree with the chart, fix tension, alignment, and groove wear first — see Pulley and Belt Problems and Solutions — then remeasure diameters.
Multi-groove drives still follow the same diameter ratio per sheave set; horsepower capacity scales with the number of belts, not the RPM formula. Matched belt sets matter when grooves share load.
Worked Examples From the Table
Compressor-style reduction3" driver, 6" driven, 1725 RPM motor → ratio 2.000:1 → ~863 RPM at the pump. Confirm the pump nameplate accepts that speed, then re-check CFM with the Air Compressor CFM Calculator.
Speed-up for a light spindle4" driver, 2.5" driven, 3450 RPM motor → ratio 0.625:1 → ~5520 RPM. Verify bearings, guards, and tool ratings before you run that fast.
Drill-press ballpark2.5" driver, 5" driven on a 1725 motor → ~863 RPM spindle. Feed that into the Drill Speed Calculator with bit diameter and material SFM.
Full theory, belt-length formula, and reverse sizing walkthroughs are in the Pulley and Belt Ratio Guide. Belt-type selection is in V-Belt vs Flat Belt vs Timing Belt.
What This Chart Does Not Replace
- Manufacturer horsepower ratings by belt section and RPM.
- Minimum pulley diameters for a given belt cross-section.
- Guard, shaft key, and taper-lock hardware specs.
- OEM maximum pump or spindle RPM.
- Exact cut-length belt numbers (use center distance + the calculator’s length estimate, then match a catalog code).
Treat every cell as a starting point. Measure, calculate, tach-verify, then lock the motor base.
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Shop Tools That Support Pulley Work
Dedicated V-belts, sheave sets, belt tension gauges, and laser tachometers are not in the current TestTalkHQ affiliate CSV — so they are not invented here. These are real catalog items you can use while sizing and checking a belt drive.
Starrett Stainless Steel Electronic Slide Caliper 0–6"
Measure driver and driven pulley outside diameters before you trust a stamped size. Pitch diameter may differ from OD on V-groove sheaves — confirm what the catalog calls out.
View on Amazon →Dial Indicator Set with Magnetic Base
Check pulley face runout and shaft end-play after a swap. A few thousandths of wobble will walk a belt off the groove and chew the sidewall.
View on Amazon →Klein Tools 935DGGP Digital Angle Gauge
Confirm sheave faces are coplanar and shafts are parallel before you tension. Misalignment is the #1 cause of squeal that “needs more tension.”
View on Amazon →GEARWRENCH 161D 32-Blade Feeler Gauge Set
Probe V-groove wear and belt bottoming. If the belt rides on the groove floor instead of the flanks, ratio and belt life both go wrong.
View on Amazon →CDI 2503MFRPH 1/2" Drive Torque Wrench
Torque taper-lock bushings and set screws to the sheave maker’s spec. Under-torque walks; over-torque cracks cast iron hubs.
View on Amazon →Makita MAC2400 Big Bore Air Compressor
Common belt-driven shop compressor — the exact use case for a pulley swap when you need more CFM headroom or quieter lower RPM.
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