Total value locked (TVL) is widely used to measure the size and popularity of decentralized finance (DeFi). However, the prevalent TVL calculation framework suffers from a "double counting" issue that results in an inflated metric. We find existing methodologies addressing double counting either inconsistent or flawed. To solve this, we formalize the TVL framework and propose a new framework, total value redeemable (TVR), to accurately assess the true value within DeFi. TVL formalization reveals how DeFi's complex network spreads financial contagion via derivative tokens, amplifying liquidations and stablecoin depegging in market downturns. We construct the DeFi multiplier to quantify the double counting, which mirrors the money multiplier in traditional finance (TradFi). Our measurement finds substantial double counting in DeFi. During the peak of DeFi activity on December 2, 2021, the difference between TVL and TVR was \$139.87 billion, with a TVL-to-TVR ratio of about 2. We further show that TVR is a more stable metric than TVL, especially during market downturns. A 25% decline in the price of Ether (ETH) leads to a \$1 billion greater non-linear decrease in TVL compared to TVR. We also observe a substitution effect between TradFi and DeFi.