Cable Pulley Ratio Calculator

Adding cables to a power rack

No cable tower yet? These rack-mounted pulley systems bolt onto uprights you already own. The same math applies: check the ratio the maker states, then run it through the calculator above. Before you order, confirm your upright size and hole diameter in the Rack Attachment Fit Checker.

Bulletproof

High/Low Pulley System (single side)

Bulletproof says it works with its VTS, VTS Lite and compatible 3×3 rack uprights. One unit covers one upright, and it sticks out up to 25.16″ in front of it.

See it at BulletproofCheck rack fit

Bulletproof

Direct Flight Multi-Flight

Bulletproof says it needs 3×3 uprights with 1″ or 5/8″ holes for rack-face mounting, and that it does not work with 2×2, 2×3 or other non-standard uprights.

See it at BulletproofCheck rack fit

Product images courtesy of Bulletproof Fitness Equipment, used with permission. I earn a commission on Bulletproof purchases made through these links, at no extra cost to you. Full disclosure.

How the math works

A cable machine is a block and tackle. A 2:1 supports the stack on two rope segments, so the handle carries half the load and travels twice as far. Force and distance trade against each other, always.

That second line matters as much as the first and is ignored almost everywhere. Matching your load across two machines tells you nothing about whether you will still have cable left at the top of the rep.

Friction does not just make it heavier

It makes the lift heavier and the lowering lighter. Friction opposes motion, whichever way the cable is moving. With system efficiency η (the product of every sheave the cable bends around):

This matters more than it looks. Eccentric loading is a meaningful driver of hypertrophy, and a long-path machine quietly takes some of it away: the harder the concentric feels, the lighter the eccentric actually is. Two machines set to the same pin can deliver noticeably different eccentric tension.

On a 1:1 there is no mechanical advantage for the drag to divide against, so the handle carries the full stack plus friction on the way up. A 1:1 lat pulldown reads heavier than the plates suggest, not lighter.

Where the efficiency figures come from

The honest position is that nobody has published a measurement of pulley efficiency for gym cable machines. Manufacturers treat it as proprietary, and sports science papers assume the nominal ratio and move on.

The closest hard numbers come from a pulley manufacturer’s own bench comparison of two near-identical rescue pulleys: 95.6% with a bearing against 91.4% with a bushing, a 4.2 point gap attributable to the bearing alone. Gym conditions should sit a little better than that, because a 4.5 inch sheave on 3/16 inch cable gives a D/d ratio of 24:1 against roughly 4:1 in rescue rigging, and bending losses fall sharply as that ratio rises. The mechanism is documented: Máté and Szekrényes measured tension loss in 7×19 cable — the same construction gyms use — over pulleys at low speed, and separated it into bearing friction and cable bending hysteresis.

So this tool uses 96–98.5% per sheave for sealed bearings and 92–95% for bushings: the measured figures nudged up for gentler gym geometry, presented as a range because a single decimal would be false precision.

What this tool does not model

The guide rods. The top plate slides on bushings around two steel rods, and there is good reason to think that drag rivals or exceeds the pulleys, particularly on a stack that is tilted or dry. It is not modelled here because there is no figure worth quoting, and inventing one would defeat the purpose.

Also unmodelled: cable stretch, the inertia of the stack itself during fast reps, and any binding from an unbalanced load. If a number matters, hang a known weight from the handle and read it on a scale.

Does sheave material change anything?

Not the resistance, no. Efficiency is set by the bearing and the sheave diameter, not by what the sheave is cast from. Aluminium, steel and nylon sheaves of the same size on the same bearing pass essentially the same load.

What material changes is inertia. A 4.5 inch steel sheave contributes roughly 1.1 lb of effective mass at the cable; the same sheave in aluminium contributes about 0.4 lb, and in nylon about 0.15 lb. Across a six-pulley functional trainer that is around 6.6 lb of equivalent mass in steel against 2.4 lb in aluminium. You only feel it while accelerating, so it is invisible on a slow grinding set and mildly noticeable on explosive work.

The tradeoff is wear. Aluminium is light but soft, and steel cable running in a soft groove will cut it over time, which is why quality aluminium sheaves are anodised or lined. Steel sheaves are heavy but take steel cable indefinitely. Nylon is the lightest and self-lubricating but the weakest. If you are choosing parts, choose the bearing first and the material second.

Plate-loaded is a different problem

Selectorized and plate-loaded machines share the same pulley math, and then diverge on four things that nobody puts on a spec sheet.

The carriage is not weightless

On a selectorized stack the top plate is part of the stack and the decal counts it. On a plate-loaded tower the horns are welded to a trolley that rides the upright, and that trolley hangs on the cable whether you load it or not. Cable tower carriages generally run 11 to 14 lb. The Rogue Rhino’s trolley is 27 lb.

The error this creates is worst exactly where precision matters most. Load 20 lb of plates on a 2:1 expecting 10 lb at the handle and an 11 lb carriage makes it 15.5 — a 55% overload. On a 5 lb target it is a 110% overload. On a 100 lb lat pulldown (1:1) the same carriage is an 11% error and barely worth mentioning — on a 2:1 the same carriage is only about a 5.5% error at 100 lb, because the ratio divides the carriage’s share too. Light isolation work on a plate-loaded machine is where training logs quietly stop meaning anything.

Almost nobody publishes this number. Put the carriage on a bathroom scale if you can get it off, or work it out by hanging a known weight from the handle and comparing.

You get continuous loading instead of fixed steps

This is the real advantage, and it is the mirror image of the micro-plate problem. A selectorized 2:1 with 10 lb plates locks you into 5 lb jumps at the handle. A plate-loaded 2:1 with 1.25 lb change plates gives you 1.25 lb jumps, and with half-pounders, 0.5 lb. No magnets, no extender pin, no aftermarket anything — your resolution is (smallest plate × number of horns) ÷ ratio. Load both horns evenly and a 1.25 lb plate on each side of a 2:1 is 2.5 lb of added plate, or 1.25 lb at the handle.

Bumper plates strangle the machine

This one is counterintuitive and it costs people real capacity. Horn sleeves run roughly 8.5 to 11 inches. A 45 lb competition bumper is about 3.5 inches thick, so you fit three per horn at best. A 45 lb cast iron plate is about 1.4 inches, so seven fit in the same space.

On an 11 inch horn at 2:1, that is the difference between roughly 140 lb and roughly 320 lb of resistance at the handle — on the identical machine, decided entirely by which plates you own. If you are loading a cable tower, thin cast iron or machined steel plates are worth more to you than bumpers, and the wide rubber discs also sit closer to the frame and are likelier to foul it.

Every plate is cantilevered

Horns stick out horizontally, so the load always sits several inches off the guide axis. Matched plates on both sides cancel the side-to-side moment but not the fore-aft one, and mismatched plates twist the carriage into its guides. Budget towers that slide on a powder-coated upright with plastic blocks rather than chrome rods with linear bearings feel this most, and it shows up as a wider gap between how heavy the lift feels and how light the lowering does.

A correction worth making

The distance half of this relationship is stated backwards in places you would expect to be reliable.

If the handle moved one foot while the stack rose two, conservation of energy requires the handle force to be twice the stack weight, not half. The first statement would be wrong.

The first statement is the correct one. On a 2:1 you feel half the stack, so the handle must travel two feet for every one foot the stack rises — the reverse of the second sentence. Halve the force, double the distance.

RitFit, to their credit, states it correctly in their own guide: “pulling the handle 2 feet raises the stack roughly 1 foot.” Same ratio, opposite description, and only one of them can be right.

This is not pedantry. It is why people match their load correctly when switching machines and then run out of cable partway through the rep. When a spec sheet and the physics disagree, measure the machine.

Ratios and increments by manufacturer

Stated ratios and real plate increments, from manufacturer sources. Two things worth noting before you read it: the increment is almost never a round 10 lb once you divide it by the ratio, and several manufacturers write the ratio reversed.

Read the Cybex row twice. On the Bravo, the numbers printed on the stack already show effective load, not physical plate weight. Put those numbers into this calculator and you will divide by the ratio a second time and end up at half the weight you wanted. Any machine with calibrated decals needs the physical plate weight, not the sticker.

Every machine the calculator knows

The calculator carries published ratios for 79 machines across 27 brands. Every figure below comes from the manufacturer’s own product page, spec sheet or manual. Where a maker publishes no ratio, the machine is not listed — an estimate would be worse than a gap, because people load bars from these numbers.

One warning before you read the table. The colon notation is not standard and you cannot trust it across brands, or even within one brand. Force USA prints “2:1” on the G1, G6, G15 and G20 to mean you feel half, then prints “1:2” on the C20 for the case where two stacks add together. Inspire uses “1:2” to mean you feel half. That is why the table has a plain-English column: read that one, not the ratio.

A machine missing from this list is not a machine without a ratio — it is a machine whose maker does not publish one. Plenty of brands sell cable equipment and never state the ratio anywhere: Freemotion, Keiser, Batca, TuffStuff and several others were checked and came back empty. If you own one of those, measure it: hang a known weight from the handle and compare it against the pin setting.

Worked examples

Common questions

Why does my 2:1 feel heavier than half the stack?

Friction, and probably path length. Half the stack is the frictionless ideal. Every sheave adds drag and the losses compound, so a functional trainer routing cable through six pulleys loses far more than a single tower through two. The same pin genuinely feels different on different machines.

Do magnetic micro plates work the same on a 2:1?

No. Weight added to the stack is divided by the ratio, so 2.5 lb of magnets moves a 2:1 handle by 1.25 lb. Weight added at the handle end is not divided at all.

My machine says 1:2, not 2:1. Which is it?

Same thing. Precor, Hammer Strength, Inspire and some Life Fitness models write the fraction the other way round. If the spec says you feel less than the stack, it behaves as this tool’s 2:1 or 4:1 regardless of which order the numbers are printed in.

How do I find my ratio without a spec sheet?

Measure it. Pull the handle a known distance and watch the stack. Handle 20 inches, stack 10 inches, you are on a 2:1. Thirty seconds, and more reliable than a spec sheet.

Is 1:1 or 2:1 better for building muscle?

Neither, if the resistance at the handle is matched. Mechanical tension is set by the force your muscle produces over the range it produces it, not by the pulley arrangement delivering it. What the ratio changes is practical: a 2:1 gives smaller effective jumps and more cable travel, a 1:1 gives bigger jumps and heavier top-end loading in a shorter range. Choose on range of motion and increment size.

Are aluminium pulleys better?

Lighter, not stronger and not more efficient. Efficiency comes from the bearing and the sheave diameter. Aluminium cuts rotational inertia, which you notice only during acceleration, and it is soft enough that steel cable will wear an unlined groove. Pick the bearing first.