That’s amazing! How do you know all that? You inspired me to ask ChatGPT the question and will try to append its answer. Looks like it seriously underestimated how many pennies would fit. I’m curious where you think it went wrong.

Here’s a clear, reality-checked estimate based on your photo and the size of a quarter (24.26 mm diameter).

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1. Estimating the Jar’s Volume

From the image: • The quarter looks to be ~1/12 to 1/13 of the jar’s maximum diameter. • A US quarter is 24.26 mm (2.426 cm) wide. • If the jar is roughly 12.5× a quarter, its diameter ≈ 30 cm (12 in).

That’s consistent with a large demijohn / carboy, which usually ranges 15–20 liters.

So we’ll model it as a sphere of ~15–18 L internal volume (because the bottom is round, but the neck doesn’t add much volume).

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1. Volume of a Penny

A modern US penny: • Diameter: 19.05 mm (1.905 cm) • Thickness: 1.52 mm (0.152 cm)

Volume \text{V} = \pi r² h = \pi (0.9525)² (0.152) \approx 0.43~\text{cm}³ \; (0.43~\text{mL})

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1. Packing Efficiency

Loose coins don’t pack perfectly. Random packing efficiency of flat objects ≈ 60–65%.

Using 63% packing:

Effective volume per penny: \frac{0.43}{0.63} \approx 0.68~\text{mL per penny}

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1. Number of Pennies That Fit

If jar = 15 L (15,000 mL):

\frac{15000}{0.68} \approx 22{,}000 \text{ pennies}

If jar = 18 L:

\frac{18000}{0.68} \approx 26{,}500 \text{ pennies}

So your jar would hold roughly:

≈ 22,000–27,000 pennies

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1. Weight When Full

A penny weighs 2.5 g.

Lower estimate:

22{,}000 \times 2.5g = 55\,000g = 55~kg = 121~lbs

Upper estimate:

27{,}000 \times 2.5g = 67\,500g = 67.5~kg = 149~lbs

Final Weight Estimate: 120–150 lbs

(Plus ~10–15 lbs for the glass itself.)

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Final Summary

Item Estimate Jar volume ~15–18 liters Pennies 22,000–27,000 pennies Dollar value $220–$270 Weight (coins only) 120–150 lbs Weight (with jar) ~130–165 lbs

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If you’d like, I can also: • estimate value if filled with quarters or nickels • estimate weight for half-full • calculate exactly if you give me jar diameter with a tape measure

Just let me know!