Weight & density comparator

Density: the number your hands already know

Pick up a steel spanner and a plastic one of the same size and your hand instantly knows which is which — that judgement is density, mass per unit of volume. The trap in everyday language is that we say heavy when we mean dense: lead is not heavier than feathers — a tonne of each weighs a tonne — but a litre of lead weighs over 11 kg while a litre of feathers barely registers on a scale. Fixing the volume is what makes the comparison meaningful, and that is exactly what this page does: one volume, every material, side by side. A few anchors are worth memorising: water is 1 kg per litre almost by definition, mild steel is about 7.85 times that, and gold — at 19.32 — nearly twenty times.

Two comparisons that decide real projects

Take the same bracket machined once in mild steel and once in aluminium: at 7.85 versus 2.70 kg per litre, the aluminium part weighs about a third of the steel one at identical dimensions — which is the entire story of why aircraft and bicycles pay a premium for the lighter metal, and why swapping material without rechecking strength is a decision, not a detail. The second classic is gold versus brass, the counterfeiter's favourite because the colour is close: the density is not. Gold sits at 19.32, brass around 8.5 — less than half — so a genuine gold item weighs more than twice as much as a brass imitation of the same size. That difference is famously how Archimedes checked a crown without melting it, and it still works today with a kitchen scale and a jug of water.

Carats: the same weight is not the same size

Gemstones are traded by weight — the carat, exactly 0.2 grams — but worn by size, and density sits between the two. A 1-carat diamond and a 1-carat ruby weigh precisely the same 0.2 g, yet the ruby is the smaller stone: ruby and sapphire, at a density of about 4.0, pack their weight more tightly than diamond at 3.52. Emerald, at 2.76, goes the other way — a 1-carat emerald looks noticeably larger than a 1-carat diamond. At the far end sits amber, barely denser than water at 1.08, which is why an amber piece of impressive size can weigh surprisingly few carats. The second calculator on this page turns any carat figure into actual volume per stone — a more honest basis for judging size than the carat number alone.

Honest limits — and the practical next step

The values here are good reference figures, not certificates. Alloys vary: steel is a family running from roughly 7.7 to 8.0 depending on grade, brass shifts with its zinc content, and wood is the extreme case — oak's figure moves with moisture, and two boards from the same tree can differ. For building intuition and rough comparison — the job of this page — none of that matters; for engineering it does, so take the number from your specific material's datasheet when the answer has consequences. And when the question turns practical — what does three metres of 40 mm bar actually weigh, and what will it cost — step over to our free Metal weight calculator, which works per shape (bar, tube, plate and more), knows the standard metals, and has a price-per-kilo field for an instant cost estimate.

Why gold feels so heavy

Weight (for a fixed volume) comes down entirely to density — how tightly the material's atoms are packed. Platinum and gold are dense metals, so even a small amount is heavy; wood and gases are the opposite, mostly empty space between light atoms, so the same volume weighs very little.