It seems most laws regarding marijuana have varying consequences based on the quantity/weight. How does this apply to extracts such as THC and CBD oils, edibles, etc? Is it based on the weight of the extracts or the rough equivalent weight of marijuana?
Starting with federal law, under 21 USC 841, there are 4 levels of trafficking weight for marijuana, the most severe being
1000 kilograms or more of a mixture or substance containing a detectable amount of marihuana, or 1,000 or more marihuana plants regardless of weight
21 USC 802(16) indicates that "marijuana" includes the plant, the leaves, the resin etc. but does exclude hemp fibers and seed-byproduct. A ton of ice cream with a milligram of marijuana would thus count for life imprisonment and $50 million fine (if it is detectable, which is a technology question). At the level of under 50 kg, the computation becomes more complex in sentencing based on weight, then excepting and separately penalizing "50 or more marihuana plants regardless of weight, 10 kilograms of hashish, or one kilogram of hashish oil". In other words, federal law generally considers any cannabinoid-bearing substance to be equal to any other such substance, and strangely either counts plants or grams, depending. Then at lower weights, distinctions are made between regular marijuana, hash, and hash oil. Simple possession doesn't distinguish what the substance is or what the weight is (because trafficking laws make those distinctions).
In Washington, marijuana possession is legal up to certain limits. Under RCW 69.50.360, these limits are:
(a) One ounce of useable marijuana;
(b) Sixteen ounces of marijuana-infused product in solid form;
(c) Seventy-two ounces of marijuana-infused product in liquid form; or
(d) Seven grams of marijuana concentrate
The underlying theory is that these are equivalent in terms of their effects. The state regulates growth and manufacturing under RCW 69.50.345, so there are rules pertaining to concentration of THC, CBD, and THC-CBD ratios. This is implemented via WAC 314-55-095 by rules such as the one that "A single serving of a marijuana-infused product must not exceed ten milligrams active tetrahydrocannabinol (THC), or Delta 9".
The general pattern is that in laws saying that marijuana is legal, there is no attempt to reduce weight limits to a constant factor such as "amount of THC", but in (state) laws allowing marijuana, an effort is made to recognize that hash oil and leaves are not functionally equivalent.