How much does the air in a classroom weigh?

Question

Air near sea level has a density of about $1.2$ kilograms per cubic metre. Picture a classroom roughly $8$ m by $8$ m with a $3$ m ceiling. Solve in your head.

Estimate the total weight (mass) of the air in the room. Aim: under 30 seconds.

Accepted Answer

Room volume: 8 	imes 8 	imes 3 = 192 	ext{ m}^3. Multiply by the density: 192 	imes 1.2 \approx 190 	imes 1.2 = 228 	ext{ kg}. So the air weighs roughly 230 kg, about a quarter of a tonne, or the mass of three adults (range 200–250 kg for reasonable room sizes). Takeaway. People imagine air as nothing, but 1.2 kg per cubic metre adds up fast in any real space. Memorising that density lets you weigh the atmosphere in any room with a single multiply.

How much does the air in a classroom weigh?

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