Needle Felting Wool Quantity Calculator
Wool for needle felting is sold by weight, but you design by size, so the link between the two is the packed density of your felted fibre: how many grams fill a given volume once needled firm. This calculator takes the bounding dimensions of your finished piece, computes the volume, multiplies by a density you measure from a test piece, and adds a compaction allowance for the fibre lost to compression and trimming. The density is your input because it depends entirely on your fibre and how hard you felt, so nothing is assumed on your behalf.
Needle felting wool formula
Volume = length * width * height
Base weight = volume * packed density
With allowance = base * (1 + compaction% / 100)
Ounces = grams / 28.3495
Packed density is grams of felted wool per cubic inch, measured from a firm test piece. One ounce (avoirdupois) is 28.3495 grams. A box volume slightly overestimates a rounded shape, which is a safe margin.
Needle felting context
- Wool is sold by weight, so the packed density links your target size to grams.
- Measure density from a firm test piece in the fibre and firmness you will use.
- Loose wool compresses greatly as you needle it; the allowance covers this and trimming loss.
- A bounding-box volume slightly overestimates a rounded form, which is a safe direction.
- One ounce is 28.3495 grams, per the NIST Office of Weights and Measures.
Needle felting wool: frequently asked questions
How much wool do I need for needle felting?
Wool weight equals the finished object's volume times the packed density of the felted wool. Density is how many grams of wool fill a unit volume once felted firm, which depends on the fibre and how hard you compact it. Measure it from a test piece and enter it; the calculator multiplies by your volume.
How do I measure packed wool density?
Felt a small firm test ball, weigh it on a scale, and measure its dimensions to find its volume. Density is weight divided by volume, for example grams per cubic inch. This single rate captures your fibre and your felting firmness, which is why it is a user input rather than a fixed number.
Why include a compaction allowance?
Loose wool compresses dramatically as you needle it, and some fibre is lost to fly-away and trimming. A compaction allowance adds a margin so you start with enough loose wool. Enter the percentage extra you want; the calculator adds it to the base weight derived from volume and density.
How do I find the finished volume?
Approximate the object as a simple shape. This calculator uses a box volume (length times width times height) as a stand-in; for a rounded form, a box that just contains it slightly overestimates, which is safe. Enter the bounding dimensions of your finished piece in inches.
Is the estimate exact?
It is a guide, not a guarantee, because felting firmness varies across a piece and fibres differ. Accuracy hinges on how representative your density measurement is. Felt a test piece in the same fibre and firmness you plan to use, and round up. Keeping notes lets you refine the density rate over projects.
Official sources
- NIST: SI units (gram and mass).
- NIST: Office of Weights and Measures.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.