Arrow Spine Calculator

Spine is the measurable stiffness of an arrow shaft, expressed as the deflection (in thousandths of an inch) the shaft bends when a 1.94 lb weight is hung from its center across a 26-inch span — the AMO/ASTM static spine standard. A spine number of 340 means the shaft deflects 0.340 inches under that load; a 500 deflects 0.500 inches. A lower number means a stiffer shaft, a higher number means a softer shaft. So when you read 'what is spine on an arrow,' the answer is: a standardized stiffness rating where the number is literally the bend in inches.

Enter your bow type (compound, recurve, or traditional), peak draw weight, draw length, finished arrow length, point weight, and — for compounds — cam type. The calculator starts from a static-spine baseline drawn from Easton and Gold Tip selection tables, then applies dynamic spine corrections: each 50gr of point weight over 100gr softens the recommendation by one grade, each inch of draw length over 28″ stiffens it, a shorter-than-28″ cut stiffens it, and a hard cam stiffens it one more grade. The output is a single recommended spine number plus a stiffness warning telling you whether the build lands optimal, slightly soft, or slightly stiff.

For a 70 lb compound bow at a 29″ draw length shooting a 100gr point, the baseline is a 340 spine. If you shoot a 125gr broadhead, soften to 400 (the heavier point weakens dynamic spine). If your bow has a hard cam with 80%+ let-off, stiffen back toward 340. If your draw length is 31″, stiffen one more grade to 300. The calculator above applies all of these corrections automatically — plug your numbers in rather than guessing from a single chart cell.

The 3 Rivers (3Rivers Archery) spine calculator is tuned for traditional and recurve shooters and cross-references draw weight against arrow length in a deflection table — it is an excellent static-spine starting point for off-the-shelf recurve builds. This calculator adds three things the 3 Rivers tool does not: a compound-bow track with cam-type correction, dynamic point-weight adjustment (±50gr = ±1 spine grade), and an automatic stiffness verdict. For traditional bows the two tools agree within one grade; for hard-cam compounds this one is more accurate.

Use both. The Easton spine chart gives you the static baseline — the deflection number Easton publishes for your draw weight × draw length combination. A dynamic spine calculator (like this one) then corrects that baseline for the things the static chart cannot see: point weight, arrow cut length, cam aggressiveness, and bow type. The static number alone ships wrong roughly 15% of the time on aggressive-cam compounds; pairing it with dynamic correction brings that error to near zero.

An arrow that is too soft (spine number too high for the bow) flexes too much on launch. Symptoms: the nock end kicks right (for a right-handed shooter), broadheads plane left and group poorly, paper-tune tears show a dramatic right tear, and arrow flight looks 'wiggly.' The fix is to stiffen — either move down one spine grade (500→400), increase point weight to weaken the static spine back toward dynamic balance, or shorten the shaft slightly (cutting stiffer).

An arrow that is too stiff (spine number too low) does not flex enough to clear the rest cleanly. Symptoms: the nock kicks left, broadheads plane right, paper-tune shows a left tear, and impact points shift left at distance. The fix is to soften — move up one spine grade (340→400), reduce point weight, or lengthen the shaft if you have room. Over-stiff arrows are the most common cause of broadhead flight issues on compound bows.

Yes. Select 'recurve' or 'traditional' as the bow type and the calculator switches to the appropriate static-spine baseline table (recurve and traditional bows need softer spines than compounds at the same draw weight because they finger-release and load the shaft differently). The cam-type field is hidden for non-compound bows since it does not apply. Traditional shooters will find the results align closely with the 3 Rivers archery spine calculator within one grade.

Yes, dramatically. Dynamic spine — how the arrow actually flexes in flight — is driven heavily by point weight. The rule of thumb is ±50 grains of point weight from a 100gr baseline equals one full spine grade: a 150gr point makes a 340 shaft behave like a 400, and a 75gr point makes a 400 behave like a 340. This is why switching from a 100gr field point to a 125gr broadhead often ruins groups until you re-tune — the shaft is now dynamically softer than it was.

Static spine is the lab measurement: 1.94 lb hung from the center of a 26″ shaft, deflection in thousandths of an inch. It is a property of the bare shaft and never changes. Dynamic spine is how stiff the arrow behaves in flight — it changes with point weight, arrow length, draw weight, cam type, and bow type. Two arrows with the same static spine (e.g. both 400) can have very different dynamic spines depending on how they are built and shot. The static number is what you buy; the dynamic behavior is what you tune.

A 350 spine sits between the standard 340 and 400 grades (Victory and Black Eagle use it as an intermediate step) and suits a 55–65 lb compound or a 50–55 lb recurve at 28–29″ draw — plug those numbers into the calculator above for a dynamic-corrected answer. A 300 spine arrow for a 60 pound bow is generally TOO STIFF for a 60 lb compound at 28–29″ draw (the correct 60 lb spine is 400); a 300 only becomes the right call at 60 lb if you shoot a 31″+ draw with an aggressive binary cam and a 125+ gr point, or you are building a high-FOC heavy-arrow hunting rig on purpose. For the full spine-number-to-draw-weight reverse table (500, 400, 340, 300, 250), see the Spine-to-Draw-Weight Reverse Lookup on the Arrow Spine Chart page.

A 1000 spine is an extremely weak (very flexible) shaft — it deflects a full 1.000″ under the AMO 1.94 lb test load, roughly twice the deflection of a 500. 1000 spine arrows are built for very light bows: youth bows in the 10–20 lb draw-weight range, lightweight target recurves under 25 lb, and some beginner club setups. They are almost never correct for an adult hunting compound (which lands in the 300–500 band). If the calculator above returns a spine in the 700–1000 range, you are likely entering a youth or very light target bow — confirm against the static deflection table on the Arrow Spine Chart page, where the .600 grade already marks the 'light / youth / traditional' band as the weakest commonly sold carbon spine.

Yes — the calculator returns a single numeric AMO spine (300 / 340 / 400 / 500 / 600) that applies identically across Victory, Gold Tip, Black Eagle and most Easton carbon lines, because all of those brands use the same AMO numbering. So a 'Victory arrow spine calculator' or 'Podium archery arrow calculator' search resolves here for the NUMBER, then to the matching brand's model list on the Arrow Spine Chart page — Victory uses a 350 intermediate grade between 340 and 400, and Podium Archery builds custom carbon shafts on the same 300–600 scale, so when the calculator returns 340 you can read it across to the Victory RIP / VAP rows or the Podium custom-build rows on that chart. The calculator itself stays brand-agnostic; the chart page is where the brand-specific model selection happens.

The three options — an online calculator like this one, phone apps, and downloadable desktop spine-and-tuning programs — all implement the same static-plus-dynamic spine math, so accuracy is driven by the input tables and correction logic, not the platform: enter the same draw weight, draw length, arrow length, point weight, and cam type anywhere and you land within one spine grade of the same answer. The differences are practical, not mathematical. Paid desktop software bundles spine selection with sight tapes, ballistics, and broadhead-tuning modules, but requires purchase, installation, and manual bow-profile setup. App-store spine calculators add portability, but correction depth varies widely between them. This online calculator needs no download or installation, runs in any phone, tablet, or desktop browser, applies the full dynamic correction set (point weight, cut length, cam type), and stays current without updates — on a phone you can add it to your home screen from the browser menu and it launches like a native app. If you want a record of the recommendation, screenshot the build card the calculator produces; the selection logic is identical across all three platforms.