Spinning Wheel Ratio Calculator
Drive ratio from whorl and drive wheel diameters.
About this calculator
A spinning wheel's drive ratio — the drive wheel's diameter divided by the whorl (pulley) diameter it's belted to — determines how many times the flyer spins for every single revolution of the treadle, and therefore how much twist you insert per unit of treadling effort. This calculator computes that ratio directly from your two diameter measurements, then multiplies it by your treadling speed in RPM to get the flyer's RPM; since each flyer revolution inserts exactly one twist, flyer RPM and twists-per-minute are the same number. Dividing twists per minute by your target twists-per-inch (TPI) tells you how fast, in inches per minute, you need to draft fiber to hit that twist level — the calculator converts this to feet per minute and yards per hour so you can pace a spinning session or estimate how long a project will take.
The drive ratio also maps to a suggested yarn weight category: low ratios under 6 suit super bulky yarn (fewer twists needed per inch), while ratios above 20 are needed for lace-weight singles that require dense twist. Swapping to a smaller whorl raises the ratio and speeds up twist insertion for finer yarns; a larger whorl lowers it for bulkier work. Keep in mind this models the mechanical relationship only — actual finished TPI still depends on how consistently you draft and treadle, and different wheels' flyer/bobbin ratios (double drive vs. scotch tension) can add further real-world variance not captured here.
Inputs
Results
Drive ratio
11
How to Use This Calculator
- Measure and enter your spinning wheel's drive wheel diameter in inches.
- Measure the whorl (pulley) diameter in inches for the whorl you are currently using.
- Enter your comfortable treadling speed in RPM (a relaxed pace is typically 50–80 RPM).
- Enter your target TPI for the singles yarn.
- Read the drive ratio and flyer RPM to understand how fast your flyer is spinning.
- Use the drafting speed in ft/min output to calibrate how fast to draft fiber for your target TPI.
How the result changes with Whorl diameter (in)
| Whorl diameter (in) | Drive ratio |
|---|---|
| 1 | 22 |
| 1.5 | 14.67 |
| 3 | 7.33 |
| 5 | 4.4 |
What each input means
- Drive wheel diameter (in)
- Diameter of the large drive wheel in inches.
- Whorl diameter (in)
- Diameter of the flyer whorl (pulley) in inches.
- Treadle speed (RPM)
- How fast you treadle — comfortable pace is typically 50-80 RPM.
- Target TPI
- Desired twist per inch for your yarn.
What each result means
- Drive ratio
- Ratio of drive wheel to whorl diameter (flyer turns per treadle turn).
- Flyer RPM
- Revolutions per minute of the flyer/bobbin.
- Twists per minute
- Number of twists inserted per minute at your treadle speed.
- Drafting speed (ft/min)
- How fast you should draft fiber to achieve your target TPI.
- Yarn output (yd/hr)
- Approximate yards of yarn produced per hour at sustained pace.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersDrive wheel diameter (in) = 22, Whorl diameter (in) = 2, Treadle speed (RPM) = 60, Target TPI = 6 = 4 input(s) provided
- Calculate Drive ratioDrive ratio = driveWheelDiameter / whorlDiameter11 = 11
- Calculate Flyer RPMFlyer RPM = treadleRpm * driveRatio660 = 660
- Calculate Twists per minute660 = 660
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does swapping to a smaller whorl let me spin finer yarn without treadling faster?
The drive ratio is the drive wheel diameter divided by the whorl diameter, so a smaller whorl produces a larger ratio for the same drive wheel. A larger ratio means more flyer revolutions — and therefore more twist — per treadle turn, which is exactly what finer, higher-twist yarns need, without you having to treadle any faster.
Why are twists per minute and flyer RPM the same number in this calculator?
Every full revolution of the flyer inserts exactly one twist into the yarn, so twists per minute is mathematically identical to flyer RPM. Flyer RPM itself is your treadle speed multiplied by the drive ratio, so a faster treadle pace or a higher-ratio whorl setup both directly raise your twist rate.
How does the calculator figure out how fast I should be drafting fiber?
It divides your twists-per-minute rate by your target twist-per-inch (TPI): fewer twists needed per inch means you can let more fiber pass through per minute at the same treadle speed. That inches-per-minute figure is then converted to feet per minute and yards per hour so you can pace a session or estimate total spinning time for a project.
Does a higher drive ratio always mean better yarn?
No — the ratio and yarn weight category are just a mechanical guide to how much twist a given whorl/wheel setup delivers per treadle turn, mapped against typical bands from super bulky (ratio under 6) up to lace weight (ratio 20+). Actual finished TPI still depends on how consistently you draft and treadle, and different wheel mechanisms (double drive vs. Scotch tension) can shift the real-world relationship beyond what the ratio alone predicts.
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