Arrow Spine Calculator (Cross-Manufacturer)
Arrow spine is set by draw weight, arrow length, point weight, bow type and cam aggression together, not draw weight alone. A 70 lb compound at 29 inch draw with a 28.5 inch arrow and 100 grain point needs roughly 340 spine.
Spine is the single setup number that decides whether your arrow flies straight, and it is also the number most likely to be answered by a company that sells shafts. This calculator is deliberately brand-neutral: it returns a static spine value in deflection, then shows you the equivalent shaft from every major manufacturer so you can shop on price, availability and grains per inch rather than on whose calculator you happened to open.
Why every other spine calculator disagrees with this one
Open the spine selector at Easton, Gold Tip, Victory or Black Eagle and you will get a recommendation for an Easton, Gold Tip, Victory or Black Eagle shaft. That is not dishonest, it is just what a manufacturer tool is for. The practical problem is that each maker calibrates its chart slightly conservatively around its own product line, so the same archer can be sent to a 340 by one and a 300 by another, and there is no neutral referee.
There is one, though, and it is the measurement itself. Static spine is a standardised physical test: the shaft is supported on two points 28 inches apart, a 1.94 pound weight is hung at the centre, and the deflection in inches is multiplied by 1,000. A shaft that sags 0.400 inches is a 400. That number is a property of the tube, not a marketing designation, so a 400 from any maker publishing deflection is the same stiffness as any other 400. This calculator returns deflection and lets you buy whatever is in stock.
The formula, shown in full
Rather than a lookup table you cannot inspect, this tool converts every input into a single effective bow weight and then reads that against spine bands. Every adjustment is listed here so you can check the reasoning or override it:
- Start with actual draw weight. For a compound that is peak weight. For a recurve, the marked weight is measured at 28 inches, so we add 2.5 pounds per inch of draw over 28 and subtract the same under it.
- Bow type. A recurve or longbow shot with fingers gets 10 pounds subtracted. The string rolls off the fingertips sideways and the shaft has to bend around a riser that is not cut past centre, so it needs to be weaker.
- Point weight. Add 5 pounds for every 25 grains above the baseline, subtract 5 for every 25 below. The baseline is 100 grains for compound and 125 grains for traditional, matching how each chart family is built.
- Arrow length. Add 5 pounds per inch over 29 inches, subtract 5 per inch under. Length is the strongest lever in the whole calculation and the one most archers underestimate.
- Cam aggression. Subtract 3 for a round wheel or genuinely smooth cam, add 5 for an aggressive speed or binary cam. A hard cam dumps energy into the shaft faster, which makes it flex more.
The result is compared against bands: under 24 pounds is 700 and weaker, 24 to 35 is 600, 35 to 45 is 500, 45 to 57 is 400, 57 to 68 is 340, 68 to 85 is 300, and above that is 250. If your effective weight lands within three pounds of a boundary the calculator says so, because that is genuinely a coin flip that tuning will decide.
Spine chart by draw weight and arrow length
This is the compound version at a 100 grain point and a medium cam. Read down your draw weight and across to your arrow length. Traditional shooters should read one column to the right, which is the same as shifting one spine group weaker.
| Draw weight | 26 in arrow | 27 in arrow | 28 in arrow | 29 in arrow | 30 in arrow | 31 in arrow |
|---|---|---|---|---|---|---|
| 30 to 39 lb | 700 | 700 | 600 | 600 | 500 | 500 |
| 40 to 44 lb | 600 | 600 | 600 | 500 | 500 | 500 |
| 45 to 49 lb | 600 | 500 | 500 | 500 | 400 | 400 |
| 50 to 54 lb | 500 | 500 | 500 | 400 | 400 | 400 |
| 55 to 59 lb | 500 | 500 | 400 | 400 | 400 | 340 |
| 60 to 64 lb | 500 | 400 | 400 | 400 | 340 | 340 |
| 65 to 69 lb | 400 | 400 | 400 | 340 | 340 | 340 |
| 70 to 74 lb | 400 | 400 | 340 | 340 | 340 | 300 |
| 75 to 80 lb | 400 | 340 | 340 | 340 | 300 | 300 |
The same spine across manufacturers
Once you have a deflection number, this table tells you what to type into any retailer's search box. Gold Tip's legacy two-number codes describe a draw weight range rather than deflection, which is why they look nothing like the others, and Carbon Express Maxima designations describe a dual-spine shaft that is deliberately stiffer at one end than the other. Both are noted rather than quietly converted.
| Deflection | Easton | Gold Tip legacy | Victory | Black Eagle | Carbon Express Maxima |
|---|---|---|---|---|---|
| 600 | 600 | 1535 | 600 | 600 | 450 |
| 500 | 500 | 3555 | 500 | 500 | 450 |
| 400 | 400 | 5575 | 400 | 400 | 350 |
| 340 | 340 | 7595 | 350 | 350 | 250 |
| 300 | 300 | 300 | 300 | 300 | 250 |
| 250 | 250 | 250 | 250 | 250 | 250 |
Victory and Black Eagle publish 350 where Easton publishes 340. That is a real 0.010 inch difference and it is small enough to be inside most tuning windows, but it is worth knowing that the two are not literally identical when someone tells you they are interchangeable.
Static spine versus dynamic spine
The number printed on the shaft is static spine and it never changes. What actually determines flight is dynamic spine: how much that shaft flexes under the specific force your bow applies, with your point weight, at your arrow length. Four things move dynamic spine and only one of them is on the shaft:
- Longer arrow, weaker. A tube supported further apart bends more. This is the largest single factor, and it is why the same 400 shaft can be correct for a 55 pound bow and a 70 pound bow depending on where it was cut.
- Heavier point, weaker. Mass at the front resists acceleration, so the shaft buckles more behind it on release.
- More draw weight, weaker. More force means more flex, which is the relationship everyone already knows.
- More aggressive cam, weaker. Two bows at the same 60 pounds can apply that force over very different time curves.
This is why a chart that asks only for draw weight cannot be right, and why the honest answer to "what spine do I need" always starts with three more questions.
A spine recommendation is a starting point, and the way you confirm it is by shooting a bare shaft alongside a fletched one at 15 to 20 yards and comparing impact points. That takes a target face that will stop a bare shaft without swallowing it and will still be usable when you move to broadheads, which is where spine errors finally show themselves.
Reading a bare shaft or paper tune result
For a right-handed shooter, a bare shaft that lands left of the fletched group, or a paper tear with the tail left, generally indicates a weak shaft. Landing right or tearing tail right generally indicates stiff. Left-handed shooters reverse both. Before you conclude anything about spine, rule out the far more common causes: centreshot, nocking point height, rest timing on a drop-away, and grip torque. Genuine spine errors are less frequent than tuning forums suggest.
If the shaft is confirmed stiff you have easy outs: add point weight, or leave the arrow longer. If it is confirmed weak your options are cutting it shorter or dropping point weight, and both of those change your front of centre and your total weight. That asymmetry is the whole argument for erring stiff.
The safety line
A badly underspined arrow is not just an accuracy problem. Under enough force a shaft that is far too weak can flex into the riser or shelf on release, and carbon that has been struck should be flexed and inspected before it is ever shot again. Combine that with the separate 5 grains per pound of draw weight minimum on total arrow mass, and you have the two hard rules of arrow building. Check total mass with the total arrow weight calculator before you commit to a build, and have a pro shop confirm anything you are unsure of.
Related tools
- Draw length calculator: get this right first, because everything downstream depends on it
- Arrow cut length calculator: turn draw length into a shaft length for your rest type
- Total arrow weight calculator: build finished grain weight from components
- Kinetic energy calculator: what the finished arrow actually delivers
- Best archery rangefinders: the accessory that fixes more misses than any arrow change
Frequently asked questions
What arrow spine do I need for a 70 lb bow?
A 70 pound compound at a 29 inch draw with a 28.5 inch arrow and a 100 grain point lands on 340 spine in almost every published chart. Move to a 125 grain point or a 30 inch arrow and the same bow wants 300. Spine is not set by draw weight alone, which is why a chart that only asks for poundage will send you to the wrong shaft roughly a third of the time.
Is a 400 spine arrow from one brand the same as another brand?
Yes, when both are labelled by deflection. Spine is a standardised physical measurement: a 28 inch span, a 1.94 pound weight hung at centre, and the deflection in inches multiplied by 1,000. A 400 from Easton, Victory or Black Eagle all bend 0.400 inches under that load. What differs is straightness tolerance, grains per inch and outsert design, none of which change the spine number.
Does a heavier point weaken arrow spine?
It weakens dynamic spine, which is the only spine that matters in flight. Static spine is a fixed property of the shaft and never changes. Adding mass at the front makes the shaft flex more on release, so the arrow behaves weaker even though the sticker still says 400. Roughly every 25 grains added to the point acts like adding 5 pounds of bow weight, and long arrows compound the same effect.
What happens if my arrow spine is wrong?
Field points hide it well, so many archers never notice until they screw on a broadhead and groups open up to a foot. A shaft that is too weak tends to plane away from the riser and shows tail-left tears for a right-handed shooter, and it is also the genuine safety concern because a badly underspined arrow can flex into the riser. Too stiff usually just costs tune and forgiveness.
Should I go stiffer or weaker if I fall between two spines?
Go stiffer. A slightly stiff shaft can be brought back into tune by adding point weight, moving the rest, or shooting a longer arrow, and all three of those are free adjustments. A shaft that is already too weak has almost no path back short of cutting it shorter or dropping point weight, both of which you may not want. Stiff is recoverable, weak is usually a repurchase.
Do recurve and compound bows use the same spine chart?
No, and using a compound chart for a recurve is one of the most common setup mistakes. A finger release makes the string roll sideways off the fingertips, so the shaft has to bend around the riser rather than leave straight from a centreshot rest. At the same marked poundage a recurve generally needs a shaft one full spine group weaker than a compound would.
How we choose: we compare published manufacturer specifications, verified owner reviews, and pro shop guidance. We do not test gear in person. Draw weight and arrow spine affect safety, so follow your bow manufacturer's specifications and have setup work checked by a qualified pro shop.