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Poundal to Newton Converter

Enter a force value and choose a direction to convert poundals and newtons.

How it is calculated

The conversion is a single multiplication or division with the fixed factor 0.138255 newtons per poundal. Poundal to newton: N = pdl × 0.138255. Newton to poundal: pdl = N / 0.138255. The direction selector decides which one is used, with poundal to newton as the default. Results are shown to 4 decimals, together with the factor itself and a line restating the pair of values. The factor follows from the definition of the poundal: 1 lb × 1 ft/s2 = 0.45359237 kg × 0.3048 m/s2 = 0.138254954… N, which the tool rounds to six decimals, so very large values carry a relative error of about three parts in ten million. A negative value is converted as it is, with its sign.

Worked example

Convert 25 poundals to newtons. Pick the poundal to newton direction and multiply: 25 × 0.138255 = 3.456375. Rounded to 4 decimals the result is 3.4564 N. Going back the other way as a check: 3.456375 / 0.138255 = 25 pdl. The reverse test on 10 N gives 10 / 0.138255 = 72.3301 pdl.

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Common mistakes

  • Choosing the wrong direction and multiplying when the value should be divided; one newton is about 7.23 poundals, not 0.138.
  • Confusing the poundal with the pound-force (lbf): a pound-force is about 4.448 N, roughly 32.17 times larger than a poundal, which is why mixing them gives a huge error.
  • Treating the poundal as a unit of mass; it is a unit of force, and the pound in its definition is a mass.
  • Rounding the result to one or two decimals before using it further, which matters because a poundal is a small force (0.138 N).
  • Reading "pdl" as a typo for "psi" or "lbs" in an old text; poundals appear only in foot-pound-second absolute-unit sources.

About this calculator

The poundal (pdl) is the unit of force in the foot-pound-second (FPS) absolute system, defined as the force needed to accelerate a 1-pound mass at 1 foot per second squared — it was devised to keep force and mass in consistent units without dragging in the gravitational “pound-force” that plagues British/American engineering unit systems. One poundal equals 0.138255 newtons in SI units.

Poundals rarely appear outside older British engineering texts and physics problems that deliberately use the FPS absolute system, but converting between poundals and newtons is still needed when working from historical technical literature or coursework that mixes unit systems. This calculator converts a force value between the two units in either direction.

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Comments (1)

  • Editorial team

    A sanity check for an old textbook answer: a 1 lb mass weighs about 32.17 poundals on Earth, because gravity is roughly 32.17 ft/s squared, and 32.17 times 0.138255 comes to 4.448 N. If your converted weight of a one-pound mass is far from 4.45 N, something went wrong. Where did you meet poundals, and which other older units would you like converted?

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