Roving Weight Calculator
Ounces of roving needed for target yardage.
About this calculator
This calculator works backward from how much finished yarn you want to how much fiber you need to buy, using McMorran's balance — a long-standing spinning-community approximation that estimates yards per pound of a yarn from its wraps per inch (WPI) squared, scaled by 100 and divided by the number of plies: yards/lb = WPI² × 100 / plies. Because that number describes finished yarn, not fiber in its unspun state, the calculator first converts your target yardage into a finished-yarn weight, then adds a waste allowance (spinning loss, sampling, leader yarn) to arrive at how much roving or top to actually purchase. The waste percentage is a manual estimate you supply — this is not measured shrinkage from any actual fiber, so if you know your prep or breed runs unusually wasteful (or unusually efficient), adjust it accordingly.
The output also rounds up to the nearest standard 4-ounce braid, since that's how most hand-dyed and commercial roving is sold, and includes a cost estimate from your entered price per ounce. Keep in mind McMorran's balance is itself an approximation developed for handspun yarns generally — actual yardage per pound varies with fiber type, spinning technique, and how tightly you spin, so a dye-lot color change partway through a braid can force you to buy more than this figure suggests. Always buy a bit extra fiber beyond the calculated total when working with a variable or hand-dyed batch.
Inputs
Results
Roving needed (oz)
0.72
How to Use This Calculator
- Enter the total yards of finished yarn you need for your project.
- Enter the target WPI of the finished yarn.
- Set the number of plies.
- Enter a waste allowance percentage to cover sampling, leader yarn, and spinning waste (5–15% is typical).
- Enter the roving price per ounce to see the estimated total cost.
- Read the total roving needed in ounces and grams, plus the number of standard 4 oz braids to purchase.
How the result changes with Target WPI
| Target WPI | Roving needed (oz) |
|---|---|
| 7 | 2.87 |
| 11 | 1.16 |
| 21 | 0.32 |
| 35 | 0.11 |
What each input means
- Target yarn yardage
- Total yards of finished yarn needed for your project.
- Target WPI
- Wraps per inch of your target finished yarn.
- Number of plies
- Number of singles plied together.
- Waste allowance (%)
- Extra fiber for sampling, leader yarn, and spinning waste (typically 5-15%).
- Roving price ($/oz)
- Cost per ounce of roving or top for cost estimation.
What each result means
- Roving needed (oz)
- Total ounces of roving/top to purchase including waste allowance.
- Roving needed (g)
- Total grams of roving/top needed.
- Finished yarn weight (oz)
- Weight of the finished yarn without waste allowance.
- Yards per pound
- McMorran's estimate of yards per pound for your yarn.
- 4 oz braids needed
- Number of standard 4 oz braids/bumps to purchase.
- Estimated cost ($)
- Total cost of roving at your specified price.
- Cost per yard ($)
- Cost per yard of finished yarn.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersTarget yarn yardage = 400, Target WPI = 14, Number of plies = 2, Waste allowance (%) = 10 = 5 input(s) provided
- Calculate Roving neededRoving needed = finishedWeightOz * (1 + wastePct / 100)0.72 = 0.72
- Calculate Roving neededRoving needed = totalRovingOz * 28.3520 = 20
- Calculate Finished yarn weightFinished yarn weight = targetYards / max(0.01, yardsPerOz)0.65 = 0.65
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
What is McMorran's balance, and why does the formula use WPI squared?
McMorran's balance is a spinning-community approximation for how much a given yarn weighs per unit length, expressed as yards per pound = WPI² × 100 ÷ plies. Squaring WPI reflects that a yarn's cross-sectional area — how much fiber a given length actually contains — scales roughly with the square of its diameter, and WPI runs inversely with diameter, so doubling WPI (a much thinner yarn) roughly quadruples the yardage from the same weight of fiber, divided further by the number of plies since each ply adds its own bulk.
Why does the calculator separate "finished yarn weight" from "roving needed"?
Finished yarn weight is the weight of the yarn after it's spun and plied, computed from your target yardage divided by the estimated yards per pound. Roving needed multiplies that by (1 + wastePct/100), because raw roving loses some material to sampling, broken ends, and leader yarn during spinning, so you always need to start with more fiber than ends up in the finished yarn.
Why does the calculator round up to 4-ounce braids?
Most hand-dyed and commercial spinning fiber is sold in standard braids or bumps, commonly 4 ounces, so the calculator takes total roving weight and rounds up to the nearest whole braid — you can't buy a partial braid, so any leftover ounces still require purchasing one more full one.
How accurate is the cost estimate?
Total cost is your entered price per ounce times the total roving ounces including waste, and cost per yard divides that total by your target yardage — both are direct arithmetic from your inputs rather than independent estimates, so their accuracy depends entirely on how accurately you've priced your roving and set the waste percentage.
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