A Unit Born From Practicality, Retired by Bureaucracy
The kilogram-force has the simplest definition of any force unit: it's the force with which one kilogram of mass presses down at standard gravity. Before SI, European engineers didn't need a force unit at all — they used the mass unit and let gravity do the arithmetic. A crane rated to lift "5 tonnes" meant 5,000 kgf of pulling force. A hydraulic cylinder spec'd at "3 t" meant 3,000 kgf. The system worked because gravity is (locally) constant, and a machine that lifts 5 tonnes on the shop floor in Lyon lifts 5 tonnes in Osaka too.
The problem SI solved — and the reason it retired kgf — is that "the force of one kilogram" changes with location. It's 9.80665 N at the standard, 9.78 N at the equator, 9.83 N at the poles, and 0 N in orbit. A force unit defined by gravity is a force unit that moves. The newton is absolute: it's defined by mass, length, and time alone — kg·m/s² — with no gravity involved. That's why every international standard since 1960 specifies force in newtons, and why the kgf lives on only in the machinery, manuals, and habits that predate the transition.
kgf = N × 0.1019716213
where 0.1019716213 = 1 / 9.80665 (standard gravity in m/s²)
1 kgf = 9.80665 N exactly — the definition of the unit.
Where You'll Still Find kgf in 2026
The unit hasn't disappeared; it's been demoted to specific habitats. European machine tool documentation — particularly German and Italian — still marks cylinder force, spring rates, and clamping force in kp or kgf, even on new equipment, because the end users ask for it. Japanese construction machinery manuals use "t" (tonne-force) for bucket breakout force and crane ratings. Chinese engineering standards retained kgf in many legacy specifications before the 1990s SI push. And the entire world's crane industry still carries dual ratings — hook capacity in tonnes (kgf) and in kN — because crane operators in Southeast Asia, Africa, and Latin America read tonnes, while the structural engineers who verify the lifts read kilonewtons.
The result is a unit conversion that never ends. A crane in Singapore rated 50 t has a hook capacity of 50,000 kgf = 490,332.5 N. The rigging engineer's software wants kilonewtons: 490.33 kN. The crane chart, printed in tonnes, says 50. The inspection report, written for the authority, might cite kN. Three documents, three unit systems, one physical capacity — and the most expensive conversion mistakes in this industry have happened at exactly this handoff, when a verification engineer trusts the label without running the number.
Common Newtons to Kilograms-Force Conversions
| Newtons | kgf | Where you'd see this |
|---|---|---|
| 1 N | 0.102 kgf | The definitional anchor — about a tenth of a kilogram-force. |
| 9.81 N | 1 kgf | One kilogram of mass under standard gravity — the exact reverse. |
| 50 N | 5.1 kgf | Bicycle brake lever force. Small pneumatic cylinder. |
| 100 N | 10.2 kgf | European handrail test load per person. Pushbutton force spec. |
| 500 N | 51 kgf | Gym machine stack force. One person hanging on a rope. |
| 1,000 N | 102 kgf | Small industrial cylinder force. European car seat belt preload. |
| 5,000 N | 510 kgf | Mid-size hydraulic press force. |
| 9,807 N | 1,000 kgf | One tonne-force — the crane rating unit. |
| 49,000 N | 5,000 kgf | Five tonnes — a small excavator bucket breakout force. |
| 98,066 N | 10,000 kgf | Ten tonnes — a typical mobile crane's mid-range lift. |
| 490,333 N | 50,000 kgf | Fifty tonnes — a serious crawler crane hook capacity. |
Worked Examples
Reading a Japanese crane chart
The chart for a Kato or Tadano crane reads "max lifting capacity 25 t." That's 25,000 kgf. Converting to newtons: 25,000 × 9.80665 = 245,166 N. The metric structural software you're verifying against wants kN: 245.17 kN. Now compare against the European spreader beam rated 250 kN: the load is 245.2 kN against a rating of 250 kN — margin 4.8 kN, about 2%. A conversion that rounds the crane's 25 t to "245 kN" instead of the exact 245.17 changes that margin by 0.07%, irrelevant; a conversion that treats "25 t" as 25,000 kg of mass and multiplies by a wrong factor changes everything.
The German machine manual with kp
A 1980s German lathe manual specifies the tailstock clamping force as "1,200 kp." The modern maintenance engineer needs newtons for the replacement parts spec. 1,200 kp = 1,200 kgf = 1,200 × 9.80665 = 11,768 N = 11.77 kN. If the engineer misreads kp as pounds (there's no good reason to, but tired eyes do strange things), the number becomes 5,338 N — a factor of 2.2 error that will underspecify the clamping system and let the workpiece shift at high spindle speeds. The kilopond-to-newton conversion is one of the quiet hazards of maintaining European machinery built before 1990.
Pneumatic cylinder: the 10-bar, 100 mm bore case
A pneumatic cylinder with a 100 mm bore at 10 bar produces a theoretical force of F = P × A = 1,000,000 Pa × π × (0.05 m)² = 7,854 N. In the language of the workshop: 7,854 N = 800.9 kgf — "about 800 kilos of push." The sales brochure will say "8 kN" (metric) or "800 kgf" (shop floor) or occasionally "1,765 lbf" (US). All three are the same force. The maintenance tech selecting a mounting bracket reads the kgf figure because that's the bracket's rating language; the automation engineer sizes the guide rod in newtons. Both are right. The conversion between them is this page.
Engineering Context
The kilogram-force has an exact, official relationship to the newton: 1 kgf = 9.80665 N, where 9.80665 is the standard acceleration due to gravity adopted by the 3rd CGPM in 1901. ISO 80000-4 (the current standard for mechanics quantities) lists the kilogram-force in its "non-SI units accepted for use" appendix — not as a recommended unit, but as a unit the world still uses, with the conversion made explicit. This is a notable difference from the pound-force, which is also non-SI but tied to a different set of treaty constants (0.45359237 and 9.80665, giving 4.4482216153). The two legacy units connect to each other exactly: 1 lbf = 0.45359237 kgf, because both are "gravity times a mass unit" and the kg/lb ratio is exact. If you're converting between the two legacy systems directly, use the lbf to kgf converter. And for the mass-to-mass conversions that people confuse with this one — how many kilograms is 50 pounds — see lbs to kg.
More: kgf to N · N to lbf · lbf to N · kgf to lbf · Force Guide
Related Unit Converters
Frequently Asked Questions
Is "tonne-force" the same as "ton-force"?
Almost, with a spelling difference that matters. Tonne-force is the metric unit: 1 tf = 1,000 kgf = 9,806.65 N, based on the metric tonne (1,000 kg). Ton-force (US short ton-force) is the customary unit: 1 tonf = 2,000 lbf = 8,896.44 N. A crane rated 25 tf lifts 245.17 kN; one rated 25 tonf (US) lifts 222.4 kN — about 9% less. When the source document says "t" or "ton," check the country: European and Asian crane charts use tonnes (tf), US charts use short tons (tonf), and British documents may use long tons (2,240 lbf). This is one of the most common unit errors in international rigging after the lbf/N confusion itself.
How do I convert kgf to newtons quickly?
Multiply by 9.81 for a quick estimate, or 9.80665 for exact values. 100 kgf ≈ 981 N (exact: 980.665). For the reverse (N to kgf), divide by 9.81, or divide by 9.80665 for precision. The common engineering shortcut — "a kilogram-force is about 10 newtons" — is off by 2%, which is fine for a first-pass estimate and not fine for a design margin. This page uses the exact 9.80665 value throughout.
Do I need kgf or kgf·m for torque?
The force unit kgf combines with a meter of lever arm to produce kgf·m, a torque unit still common in Japanese and older European specs — it's the force-side of the torque family on this site. 1 kgf·m = 9.80665 N·m exactly. If you're converting torque values from Japanese manuals (which often use kgf·m for cylinder head bolts) to newton-meters, use the kg·m to N·m converter — it multiplies by the same 9.80665 constant this page uses for pure force. The torque and force pages are two halves of the same unit family.