Poundals to Newtons: 1 pdl equals 0.138255 N. To convert poundals to newtons, multiply by 0.138255 (N = pdl × 0.138255). For example, 10 pdl = 1.38255 N.
How to Convert Poundals to Newtons
To convert from poundals to newtons, multiply the value by 0.138255. The conversion is linear, meaning doubling the input doubles the output.
Conversion Formula
- Poundals to Newtons:
N = pdl × 0.138255 - Newtons to Poundals:
pdl = N ÷ 0.138255
Poundals to Newtons Conversion Chart
| Poundals (pdl) | Newtons (N) |
|---|---|
| 0.1 | 0.013825 |
| 0.25 | 0.034564 |
| 0.5 | 0.069127 |
| 1 | 0.138255 |
| 2 | 0.27651 |
| 3 | 0.414765 |
| 5 | 0.691275 |
| 10 | 1.38255 |
| 20 | 2.7651 |
| 25 | 3.456375 |
| 50 | 6.91275 |
| 100 | 13.8255 |
| 250 | 34.56375 |
| 1000 | 138.255 |
Understanding the Units
What is a Poundal?
A poundal equals approximately 0.138255 newtons — the force needed to accelerate one pound-mass by one foot per second squared.
Common contexts: absolute foot-pound-second system.
What is a Newton?
The newton is the SI derived unit of force, equal to the force needed to accelerate one kilogram by one meter per second squared (1 N = 1 kg·m/s²).
Named after Sir Isaac Newton (1643–1727), whose three laws of motion underpin classical mechanics.
Common contexts: mechanics, engineering.
Real-World Reference Points
| Item | Poundals (pdl) | Newtons (N) |
|---|---|---|
| Weight of an apple (≈100 g) | 7.233 | 1 |
| Weight of 1 kg on Earth | 70.9558 | 9.81 |
How to Convert Poundals to Newtons
To convert poundals to newtons, multiply by 0.138254954376. The factor comes directly from the poundal\'s defining equation, F = m × a, applied to one pound-mass and one foot per second squared: 0.45359237 kg × 0.3048 m/s² = 0.138254954376 kg·m/s² = 0.138254954376 N. Every constant in that chain is defined exactly, so the conversion factor is exact, not measured.
Conversion Formula
- Poundals to Newtons: N = pdl × 0.138254954376
- Newtons to Poundals: pdl = N × 7.2330138512
- Bridge to pound-force: 1 lbf = 32.17404856 pdl (the numerical value of g in ft/s²)
For everyday work, six decimal places (0.138255) match or exceed any practical measurement precision. The full eight-decimal expansion (0.13825495) is useful only when chaining through several conversions in scientific or calibration contexts.
Common Conversions
| Poundals (pdl) | Newtons (N) | Pound-force (lbf) |
|---|---|---|
| 1 | 0.1383 | 0.0311 |
| 5 | 0.6913 | 0.1554 |
| 10 | 1.3825 | 0.3108 |
| 16 | 2.2121 | 0.4973 |
| 25 | 3.4564 | 0.7770 |
| 32.174 (1 lbf) | 4.4482 | 1.0000 |
| 50 | 6.9127 | 1.5540 |
| 70.932 (1 kgf) | 9.8067 | 2.2046 |
| 100 | 13.8255 | 3.1081 |
| 250 | 34.5637 | 7.7702 |
| 500 | 69.1275 | 15.5404 |
| 1,000 | 138.2550 | 31.0809 |
| 2,500 | 345.6374 | 77.7022 |
| 5,000 | 691.2748 | 155.4044 |
Understanding the Units
What Is a Poundal?
The poundal is the coherent force unit of the absolute foot-pound-second system. It is defined as the force that produces an acceleration of 1 ft/s² in a body of 1 pound-mass. Unlike the pound-force, the poundal contains no embedded gravitational acceleration — making it the FPS analogue of the SI newton. The unit is small by design: 1 pdl = 0.138 N, so an ordinary apple (≈ 1 N) weighs around 7 pdl.
What Is a Newton?
The newton (N) is the SI derived unit of force, equal to 1 kg·m/s². Both the newton and the poundal are absolute units in the sense that neither carries a hidden factor of gravity. The newton has won the engineering battle largely because the SI base units (kg, m, s) produce more convenient orders of magnitude for everyday forces than do the FPS base units (lbm, ft, s).
Why "Absolute" Matters
An absolute unit system defines force kinematically — purely through mass and acceleration — with no reference to local gravity. A gravitational system (kgf, lbf) defines force as the weight of a given mass at a fixed standard gravity. Both systems are correct, but they cannot be mixed casually: one pound-mass weighs 1 lbf, but in absolute terms that same weight is 32.174 pdl — a discrepancy that catches first-year physics students every semester.
Real-World Poundal References
Because the poundal is small, ordinary forces produce three- or four-digit poundal values. Some anchors to build intuition:
| Source of Force | Poundals (pdl) | Newtons (N) |
|---|---|---|
| US quarter coin (5.67 g) weight | 0.40 | 0.056 |
| One AA battery (23 g) weight | 1.63 | 0.226 |
| Standard apple (100 g) weight | 7.09 | 0.981 |
| One pound-mass weight (1 lbf) | 32.17 | 4.448 |
| One kilogram-mass weight (1 kgf) | 70.93 | 9.807 |
| Hand grip strength, adult average | 2,000–2,500 | 275–345 |
| Bicycle brake hand-lever force | 500–1,500 | 69–207 |
| Bullet base, 9 mm peak chamber pressure | ~21,700 | ~3,000 |
| Rifle peak chamber pressure on bullet base | ~108,500 | ~15,000 |
| Compact-car peak braking force | ~50,600 | ~7,000 |
Engineers handling these numbers daily would naturally migrate to a larger unit — pound-force or kilonewton — which is exactly what happened historically. The poundal\'s niche today is pedagogical, not practical.
Poundals in Education and Ballistics
The poundal is a teaching unit in disguise. By keeping mass in pounds and inserting a small force unit, it lets instructors demonstrate F = m × a without invoking the slug or apologising for the appearance of g. A canonical problem: a 50-pound-mass crate slides on a horizontal surface; a 20-pdl horizontal force is applied. Acceleration is 20 pdl ÷ 50 lbm = 0.4 ft/s² — direct, dimensionally clean, no g in sight. The same problem in SI gives 2.77 N ÷ 22.68 kg = 0.122 m/s², which checks out (0.4 ft/s² × 0.3048).
External and internal ballistics texts from the early 20th century occasionally used poundals for force-on-base of projectiles, mostly because mass-in-grains and acceleration-in-feet-per-second-squared paired naturally with the unit. Modern ballistic codes work entirely in SI, but historical reference data — Hatcher\'s Notebook, older British military proof reports — still appears in poundals and must be converted before comparison.
Related Force Converters
- Newtons to Poundals — the reverse direction
- Pounds-force to Newtons — Imperial gravitational equivalent
- Newtons to Pounds-force — opposite gravitational direction
- Dynes to Newtons — the CGS absolute counterpart
- Kilonewtons to Newtons — larger SI step
Brief History of the Poundal
The poundal was proposed in 1879 by James Thomson at the British Association for the Advancement of Science meeting in Dublin. Thomson, a Belfast-born engineer and elder brother of Lord Kelvin, wanted an Imperial force unit that would let Newton\'s second law operate without the awkward gravitational constant required when working directly in pound-mass and pound-force. His solution — keep mass in pounds, define a new small force unit equal to 1 lbm·ft/s² — fitted the Victorian engineer\'s preference for retaining familiar mass units while still building a "coherent" mechanical system.
For half a century the poundal coexisted comfortably with the pound-force in British engineering and physics curricula. The growing dominance of the metric system from the 1890s onward, and the formal adoption of SI in 1960, gradually retired the poundal from professional use. Today the unit is a curiosity — useful for reading historical literature, decoding old physics problems, and appreciating the conceptual gap between absolute and gravitational force unit systems.