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If you are buying a face cord, divide the depth of a full cord by the piece length of the wood in your face cord. Multiply this quotient by the price of your face cord to determine the cost of the full cord.  Remember that the depth of a full cord is 4 feet (1.2 m) or 48 inches (1.2 m or 122 cm). For instance, if Bob is selling a face cord with an average piece length of 16 inches (40.6 cm) for $90, the calculation would look something like this:  48 inches (122 cm) / 16 inches (40.6 cm) = 3 3 * $90 = $270 The full cord value would be $270. If you know the average market rate of a full cord in your area, you can compare the full cord value of the face cord you measured to that. If you do not know the average cost, however, you might need to shop around some and figure out your own average.  It might save time to call each dealer and ask for their face cord price and piece length measurement, rather than going to each one and taking your own measurements. You should still measure the average piece length of the face cord you plan to buy once you've made your decision, though, just to make sure that the dealer's measurements match your own. If the piece length offered by each dealer is the same, you can compare face cord costs. If the piece lengths vary, however, you need to calculate the full cord value of each and compare those values to one another.  In the previous example, Bob sold firewood at a full cord value of $270. If Sally sold 12-inch (30.5-cm) long pieces of firewood at $70, the full cord value would be:  48 inches (122 cm) / 12 inches (30.5 cm) = 4 4 * $70 = $280.   If Sam sells 8-inch (20-cm) long pieces of wood at $60, the full cord value would be:  48 inches (122 cm) / 8 inches (20 cm) = 6 6 * 60 = $360   Even though Bob has the highest face cord price, he has the lowest full cord value at $270. Sally's full cord value is close at $280, but Sam's full cord value is by far the most expensive at $360, even though Sam's face cord cost was cheapest ($60). As such, the best value for your money would be Bob's face cord. Even though full cord value is the best way to get the best deal, there are other factors to consider that usually increase the value and cost of wood.  Shorter lengths usually cost more because of the cost of cutting and handling. Firewood cut into consistent lengths may cost more because more work went into maintaining that even length. Finely split pieces usually cost more because of the extra labor, as well. Dry wood can cost more because it has been stored under better conditions. Cleaner firewood is also more valuable because it is more pleasant to the consumer when it comes time to burn it.
Calculate the full cord value. Shop around. Compare the value offered by each seller. Be aware of outside factors that can affect cost.