About WhatSizeCalc

WhatSizeCalc answers one question people ask before buying almost anything for their home: what size do I need? Each calculator turns your measurements into a clear answer, in seconds, with no sign-up.

How we work out the answers

Every calculator follows a published method, and each page names its source:

• Air conditioners: the ENERGY STAR room air conditioner sizing chart and its adjustments
• Water heaters: the U.S. Department of Energy's First Hour Rating method
• Dehumidifiers: the AHAM sizing chart, converted to the 2019 DOE test scale
• TVs: SMPTE and THX field-of-view guidelines
• Generators: running plus surge watts, from published wattage charts
• Rugs, ceiling fans and Christmas trees: widely used design and retailer sizing rules

We show the working behind each result so you can check it. Results are estimates: always measure your space and check the label on the product you buy.

Our calculators

• Rug size calculator
• TV size calculator
• Ceiling fan size calculator
• Christmas tree size calculator
• Generator size calculator
• AC size calculator
• Water heater size calculator
• Dehumidifier size calculator
• Paint calculator
• Vanity mirror size calculator
• Art over bed size calculator
• Coffee table size calculator
• Space heater size calculator
• Mini split size calculator

How the site is funded

WhatSizeCalc is free. We may show ads and earn a commission when you buy through some product links, at no extra cost to you. This never changes the answers a calculator gives.