Calculate chest fly machine to dumbbell fly weights, or vice versa, using pec deck, cable or plate-loaded settings in lbs or kg, with pulley ratios.
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Chest Fly Machine to Dumbbell Fly Conversion Formula
This calculator uses a two-step model: (1) estimate the per‑arm handle load from what your machine displays (shared stack vs per‑arm, plus pulley ratio), then (2) apply a machine‑type factor to estimate an equivalent dumbbell fly weight per hand.
\begin{aligned}
H &= \frac{MW}{A \cdot PR} \\
DB &= H \times F \\
MW &= \frac{DB}{F} \times A \cdot PR
\end{aligned}Variables:
- MW is the machine weight shown on the stack/plates
- A is the “arms” display factor (A = 2 if the display is total/shared for both arms, A = 1 if it’s per‑arm)
- PR is the pulley ratio at the handle (e.g., PR = 2 for a 2:1 cable system)
- H is the estimated per‑arm handle load
- F is the conversion factor (varies by machine type; examples used in the calculator defaults include ~0.45 for pec deck, ~0.55 for plate‑loaded fly, and ~1.00 for many cable setups)
- DB is the estimated dumbbell fly weight per hand
Because machines differ (lever arms, cam profiles, friction, range of motion, and labeling), F is not universal. Use the calculator’s machine type options and (if possible) the “Personalize Factor” tab for a closer estimate.
| Per‑Arm Handle Load (kg) | Pec Deck (F = 0.45) | Plate‑Loaded (F = 0.55) | Cable (F = 1.00) |
|---|---|---|---|
| 10 | 4.50 | 5.50 | 10.00 |
| 15 | 6.75 | 8.25 | 15.00 |
| 20 | 9.00 | 11.00 | 20.00 |
| 25 | 11.25 | 13.75 | 25.00 |
| 30 | 13.50 | 16.50 | 30.00 |
| 35 | 15.75 | 19.25 | 35.00 |
| 40 | 18.00 | 22.00 | 40.00 |
| 45 | 20.25 | 24.75 | 45.00 |
| 50 | 22.50 | 27.50 | 50.00 |
| 55 | 24.75 | 30.25 | 55.00 |
| 60 | 27.00 | 33.00 | 60.00 |
| 65 | 29.25 | 35.75 | 65.00 |
| 70 | 31.50 | 38.50 | 70.00 |
| 75 | 33.75 | 41.25 | 75.00 |
| 80 | 36.00 | 44.00 | 80.00 |
| 90 | 40.50 | 49.50 | 90.00 |
| 100 | 45.00 | 55.00 | 100.00 |
| 110 | 49.50 | 60.50 | 110.00 |
| 120 | 54.00 | 66.00 | 120.00 |
| 140 | 63.00 | 77.00 | 140.00 |
| To use this table, first estimate per‑arm handle load: if your machine shows total/shared for both arms, divide MW by 2; then divide by the pulley ratio at the handle (e.g., 2:1). | |||
What is the Chest Fly Machine to Dumbbell Fly Conversion?
This conversion provides an estimated equivalence between the weight used on a chest fly machine and the weight used for dumbbell flyes. Due to differences in resistance mechanics and stabilization factors, free weight dumbbell flyes typically require a lower load than the machine setting.
How to Calculate the Dumbbell Equivalent?
Follow these steps to perform the conversion:
- Choose your unit (kg or lbs) and identify whether the machine display is total/shared for both arms or per‑arm.
- Identify (or estimate) the pulley ratio at the handle (common cable stations are often around 2:1).
- Compute per‑arm handle load: H = MW ÷ A ÷ PR (A = 2 for total/shared, A = 1 for per‑arm).
- Choose a machine‑type factor F (or use a personalized factor): DB = H × F.
- To convert dumbbells back to a machine display setting: MW = (DB ÷ F) × A × PR.
- Verify your result using the calculator above (and adjust based on your equipment and feel).
Example Problem:
Example (cable station): If the machine shows 100 lbs total for both arms, and the cable is 2:1, then per‑arm handle load is:
H = 100 ÷ 2 ÷ 2 = 25 lbs per arm
If you assume a cable factor of F = 1.0, then the estimated dumbbell fly per hand is:
DB = 25 × 1.0 = 25 lbs
