1
kg
1,000
g
1,000,000
mg
2.204623
lb
35.273962
oz
0.001
t
0.068522
slug
15,432.3584
gr
0.45359237
kg/lb
1
kg
1,000
g
1,000,000
mg
2.204623
lb
35.273962
oz
0.001
t
0.068522
slug
15,432.3584
gr
0.45359237
kg/lb
The Mass Conversion Calculator converts mass values between eight units: kilograms, grams, milligrams, pounds, ounces, metric tonnes, slugs, and grains. Mass is a fundamental property of matter that quantifies its resistance to acceleration — it is distinct from weight, which is the gravitational force on a mass:
$$W = mg$$
The SI unit of mass is the kilogram (kg), redefined in 2019 via the Planck constant ($$h = 6.62607015 \times 10^{-34}$$ J·s). The gram (g) and milligram (mg) are decimal sub-units for laboratory and pharmaceutical use. The metric tonne (t) equals 1000 kg, used for large-scale industrial and shipping measurements.
In US customary and imperial systems, the pound (lb) and ounce (oz) are standard. The avoirdupois pound is defined as exactly 0.45359237 kg, and one pound equals 16 ounces. The grain (gr) is the smallest traditional unit of mass, originally based on a grain of wheat: 1 grain = 64.79891 mg exactly. It remains the standard unit for bullet weights and pharmaceutical dosing.
The slug is the US customary unit of mass in the force-length-time (FPS) system. It is defined as the mass that accelerates at 1 ft/s² when a force of 1 pound-force is applied:
$$1\text{ slug} = 1\text{ lbf·s}^2/\text{ft} = 14.5939\text{ kg}$$
Slugs appear in aerospace engineering, fluid dynamics, and structural analysis when working in imperial units. They resolve the confusion between pound-mass and pound-force by providing a distinct unit of mass that makes Newton's second law dimensionally consistent in FPS units.
This calculator converts any input to all eight units simultaneously by normalizing to kilograms first. It is essential for physics, engineering, pharmacy, ballistics, and international trade where different mass units are encountered.
The calculator uses the kilogram as the normalization hub:
Step 1 — Normalize to kilograms:
$$kg_{base} = \begin{cases} value & \text{from kg} \\ value / 1000 & \text{from g} \\ value / 10^6 & \text{from mg} \\ value \times 0.453592 & \text{from lb} \\ value \times 0.0283495 & \text{from oz} \\ value \times 1000 & \text{from t} \\ value \times 14.5939 & \text{from slug} \\ value \times 6.47989 \times 10^{-5} & \text{from gr} \end{cases}$$
Step 2 — Convert to each target:
$$\text{g} = kg_{base} \times 1000, \quad \text{lb} = kg_{base} / 0.453592$$
$$\text{slug} = kg_{base} / 14.5939, \quad \text{grain} = kg_{base} / 6.47989 \times 10^{-5}$$
A paperclip weighs about 1 g. A litre of water has a mass of 1 kg. An average adult human is 60–80 kg (132–176 lb). A car is about 1.5 tonnes. One slug equals about 14.6 kg — roughly the mass of a medium-sized bowling ball. A single grain is about 65 mg — the mass of a small vitamin tablet or a .22 caliber bullet at 40 grains (2.6 g).
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A 75 kg person weighs about 165.3 pounds or 5.14 slugs. Their mass equals 75 million milligrams or roughly 1.16 million grains.
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A 150-grain bullet (typical 7.62 mm NATO) has a mass of about 9.72 g or 0.343 oz — less than a third of an ounce.
Mass is an intrinsic property measuring the amount of matter, measured in kilograms. Weight is the gravitational force on that mass: W = mg, measured in newtons. A 70 kg person has the same mass everywhere but weighs 686 N on Earth (g = 9.81 m/s²), 114 N on the Moon (g = 1.62 m/s²), and 0 N in free-fall. Scales measure weight but are calibrated to display mass assuming standard gravity.
A slug is the imperial unit of mass defined so that Newton's second law (F = ma) works directly with pound-force and feet/s². One slug = 14.5939 kg. It is used in US aerospace engineering, structural dynamics, and fluid mechanics. The slug eliminates the need for the gravitational constant gc that arises when using pound-mass with pound-force.
The grain has been used for measuring small masses since antiquity (originally the mass of a grain of wheat or barley). Ballistics adopted it because bullets and propellant charges involve small, precise masses where grams would require many decimal places. A 9 mm bullet is typically 115–147 grains (7.5–9.5 g). One grain = 64.79891 mg exactly.
Until 2019, the kilogram was defined by a physical platinum-iridium cylinder in Paris. The 2019 SI redefinition fixed the Planck constant at exactly $$h = 6.62607015 \times 10^{-34}$$ J·s, which implicitly defines the kilogram through the relationship between energy, frequency, and mass (via E = mc² and E = hf). This ensures the kilogram is based on a fundamental constant, not a physical artifact.
A metric tonne (t) = 1000 kg exactly. A US (short) ton = 2000 lb = 907.185 kg. A UK (long) ton = 2240 lb = 1016.05 kg. The metric tonne is about 10% heavier than a short ton and about 1.6% lighter than a long ton. This calculator uses the metric tonne. Always verify which "ton" is meant in specifications.
For quick mental math: 1 kg ≈ 2.2 lb. To convert kg to lb, multiply by 2.2. To convert lb to kg, divide by 2.2 (or multiply by 0.454). For example, 100 lb ≈ 45.4 kg, and 80 kg ≈ 176 lb. The exact factor is 1 lb = 0.45359237 kg.
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