Math

Convert Between Any Units

Built by Kevin Glover · @gloverbuilds · Verified formula

Convert length, weight, volume, temperature, and area. Metric to imperial and back.

📅 Updated April 2026 ✅ Formula verified 📖 4 min read 🆓 Free · No sign-up

In this article

Essential Conversions
Quick Mental Math Tricks

Essential Conversions

Length: 1 inch = 2.54 cm. 1 foot = 30.48 cm. 1 meter = 3.281 feet. 1 mile = 1.609 km. Weight: 1 lb = 0.4536 kg. 1 kg = 2.205 lbs. 1 oz = 28.35 grams. Volume: 1 gallon = 3.785 liters. 1 liter = 0.264 gallons. 1 cup = 236.6 ml. Temperature: F = C × 9/5 + 32. C = (F - 32) × 5/9.

Quick Mental Math Tricks

km to miles: multiply by 0.6 (100 km ≈ 60 miles). kg to lbs: multiply by 2.2 (70 kg ≈ 154 lbs). cm to inches: divide by 2.5 (180 cm ≈ 72 inches). C to F: double and add 30 for a rough estimate (20°C ≈ 70°F). These approximations are within 5% and useful for quick conversions.

⚡ CalcWolf Insight

NASA lost a $125 million Mars orbiter in 1999 because one team used metric units and another used imperial. The spacecraft entered Mars atmosphere at the wrong angle and burned up. This remains the most expensive unit conversion error in history.

Frequently asked questions

Why does the US use imperial units?▾

The US Customary system was inherited from the British Imperial system. Congress authorized metric adoption in 1975 but made it voluntary. Industry resistance and public familiarity prevented widespread adoption. The US is one of only three countries (with Liberia and Myanmar) not officially using the metric system.

Which is more accurate: metric or imperial?▾

Neither is inherently more accurate — both can measure to arbitrary precision. Metric is easier to convert between units (everything is base-10: 1 km = 1,000 m = 100,000 cm). Imperial conversions are irregular (1 mile = 5,280 feet = 63,360 inches). Science and medicine worldwide use metric for this reason.

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Kevin Glover · @gloverbuilds

Founder, CalcWolf · GLVTS · Blickr

All formulas sourced from primary references — IRS publications, peer-reviewed research, and official standards. Results are tested against independent reference calculators before publishing. Rates and brackets updated when official sources change. Editorial policy →