Better protectors exceed ratings of 1,000 joules and 40,000 amperes. This is 10-20 joules per kilogram. The gallon gasoline equivalent is defined as 33.7 kWh, or about 1.213 joules. Power is measured in "watts", or "joules per second". Common units for selling by energy content are joules or therms. Energy is measured in "joules", or "watt seconds". The latent heat of water is 334 joules/gram. Airguns up to 17 Joules of muzzle energy are unregulated. The solution will be (in SI units) in Joules per cubic metre. Airsoft guns with under two joules muzzle energy are legal. However, most airsoft guns have much lower muzzle energy than 16 Joules. Any capacitor that can store 50 joules or more should be considered potentially lethal. Exergy and energy both have units of joules. In the SI system of measurement, work is measured in joules (symbol&colon; J). Minors (under 18) can only buy airsoft guns that are under 0.08 joules in power.