Question: What size basement pump do I need? How do I choose the right size sump pump?
Answer: Sizing a sump pump is a little tricky. To figure out how big of a sump pump you need, test your pump on a rainy day. Run your existing sump pump until the water recedes to the shutoff level. Then temporarily turn the sump pump off for one minute by unplugging it and measure how far the water rises inside the sump pit in that minute. Use a timer. Most basement sump pits will receive 20 gallons of water, or 20 inches, in one minute's time. Multiply the number of inches by 60 to estimate the volume of water per hour. Multiply that figure by 1.5 to build in a safety factor for your pumping capacity.
Your equation should look like this: inches water rose x 60 minutes x 1.5 = gallons per hour capacity required.