Most release sizing guides are written by people who haven't measured anything. They repeat manufacturer specs where specs exist (which is rare) and fill the gaps with forum impressions and guesswork. Every dimensional figure on ArcheryRelease.com comes from a physical release measured with digital calipers. This page explains exactly what we measure, how we define each dimension, and why.
All measurements are taken to 0.001" resolution using the same instrument across all releases to eliminate inter-tool variance. Measurements are taken on production releases purchased at retail, not press samples, not prototype units.
All primary dimensions are in inches. Centimeter conversions are provided for international reference at 1 inch = 2.54 cm.
Each measurement is taken three times. We record the average. If any two readings differ by more than 0.005", we take a fourth measurement and review the technique before proceeding.
Where a manufacturer publishes official dimensions, we cross-reference our measurements against them and note any discrepancy. Where no official data exists (the majority of releases on the market), our measurements are the primary source.
The bottom of the first finger groove is the point where the base of your index finger contacts the handle, the lowest structural contact point between hand and release. The hook assembly top is measured with the hook in the closed (cocked) position.
Head length is the dimension that most directly affects effective draw length and anchor position. A longer head moves your hand forward relative to the hook, which shifts your anchor point and reduces effective draw length. Most archers feel this as lost arrow speed and a changed peep alignment. For a given archer, every additional 0.25" of head length typically costs 0.25–0.50" of effective draw length depending on anchor style, which translates to roughly 5 fps at hunting weights.
This is why short-head releases like the Carter Too Simple are deliberately designed that way: hunters and short-draw archers recover draw length and speed. It's also why switching from a Carter to a Stan Onnex often requires a peep height adjustment even when the physical size of the release feels identical.
This is perpendicular to head length. If head length is the y-axis (hook assembly height relative to the finger grooves), overall length is the x-axis, the full length of the release along the direction the handle runs through your hand. It is not measured to the hook; it is measured to the furthest extent of the body itself.
Overall length gives a complete picture of how much real estate the release occupies in your hand along the draw axis. It's a secondary fit dimension (head length matters more) but it's useful for direct release-to-release comparisons and for understanding how a release will sit relative to something you already shoot.
These are the two metacarpophalangeal (MCP) knuckle prominences closest to the palm on the back of the hand. Measure with the hand palm-down on a flat surface, fingers together and relaxed, using digital calipers or a ruler.
Our sizing algorithm converts this measurement to a target groove spacing. The conversion accounts for the geometric difference between knuckle position on the back of the hand and finger groove contact on the front.
Knuckle spacing is the primary predictor of release fit for handheld thumb button releases because it directly corresponds to the 1→2 groove span, which is the dominant fit variable. It is more precise than palm circumference for this purpose because it measures the specific geometry that contacts the release, not the overall hand width.
This dimension determines how a given head length sits in the archer's hand. An archer with a proximal phalanx measurement under 1.25" will feel a long-head release more acutely at anchor. Coming from a short-head release like the Carter Too Simple (1.25" head), moving to an Onnex Large (1.50" head) typically costs roughly half an inch of effective draw length, around 5 fps. Some archers lose closer to a full inch depending on anchor position. An archer with a longer proximal phalanx has more tolerance for variation in head length across releases.
We record each inter-groove distance separately: index to middle (1→2), middle to ring (2→3), and ring to pinky (3→4) where applicable. We do not publish a single aggregate "finger span" because groove spacing is not uniform: the 1→2 gap is consistently wider than 2→3, which is wider than 3→4. On a physically measured Stan Onnex Large, these are 1.375", 1.00", and 0.75" respectively. Collapsing this into one number obscures meaningful differences between releases.
Finger span is the primary fit variable for handheld releases. Two releases can have the same overall length and head length but feel completely different in the hand because their groove spacing is different. This is the dimension that drives sizing decisions, and it's the one almost no manufacturer publishes.
Deeper grooves create a more positive finger lock. Shallower grooves allow more lateral movement. This affects both consistency at anchor and how secure the release feels under high draw weights. Some archers prefer a shallow groove for a more relaxed grip; others need the positive lock of a deep groove to achieve consistent hand placement. We measure depth to the nearest 0.001" using the depth blade of the caliper.
For releases that ship with multiple post lengths, we measure and publish each option separately.
Post length controls how far the thumb barrel sits from the back of the handle. A longer post moves the barrel further from the handle, which suits archers with a longer thumb or a more open grip angle. A shorter post positions the barrel closer in, which suits a more closed or compressed grip. Getting the post length wrong for your thumb proportions means your thumb has to work to find the barrel on every shot rather than falling naturally to it.
For releases that ship with multiple barrel sizes, we measure and publish each separately. The Stan Onnex, for example, ships with two barrels (7/16" and 5/8" diameter) and two post lengths (1" and 1¼").
Barrel diameter determines the contact geometry between your thumb and the trigger. A larger diameter creates a broader contact patch, which suits archers who fire with the pad of the thumb. A smaller diameter creates a more precise point contact, which suits archers who prefer to feel a defined trigger point. Neither is universally better; the right choice depends on your shot process and how you address the trigger.
We don't publish trigger pull weights. Trigger tension on adjustable releases varies with the user's setting, and reporting a single number from a production unit set to factory default gives a false impression of a fixed specification. We describe the adjustment range instead.
We don't publish release weight. Weight varies between aluminum and heavy metal or stainless variants of the same model. Where weight is a meaningful differentiator (and it is, particularly for target shooting), we note the material and explain the tradeoff rather than quoting a gram or ounce figure that applies to only one variant.
Three hand dimensions determine release fit: palm breadth (primary size), finger reach (head length compatibility), and middle finger length (glove size cross-check). Upload a photo of your hand and our tool measures all three automatically.
Glove size is reported as a secondary output of the AI hand measurement tool. We use the standard glove sizing chart as the reference standard because it is one of the few charts that publishes both width (circumference at MCP) and length (fingertip to palm crease) for all three tables. Width and length are cross-checked independently: if they agree, that size is reported; if they differ by one size, the larger is used; if they differ by two or more, the result flags unusual hand proportions.
Men's and Unisex tables are identical on the S12 chart and are reported as a single recommendation. Women's is reported separately.
Width is measured as circumference around the palm at the base of the knuckles, excluding the thumb. Length is measured from the tip of the middle finger to the crease at the base of the palm.
When we publish a sizing guide for a specific release, the dimensional data in that guide comes from this measurement protocol. The cross-manufacturer comparison tables are built from the same measurements taken across all releases, not from manufacturer specs mixed with forum impressions.
The goal is a single consistent dataset that lets any archer compare any two releases on the same footing. No other source does this. We built it because we needed it ourselves.