Unit Converter - Length, Weight, Temperature & More

Formula

Value in Target Unit = Value in Source Unit × (Target Factor / Source Factor)

Convert through a base unit. Divide by the source factor to get the base value, then multiply by the target factor. Temperature requires special formulas due to offset scales.

Worked Examples

Example 1: Recipe Conversion

Problem:A European recipe calls for 500 grams of flour. How many cups is that?

Solution:500 grams of flour ≈ 4 cups (all-purpose flour) Note: Cup measurements vary by ingredient: - Flour: ~125g per cup - Sugar: ~200g per cup - Butter: ~227g per cup For precision, weight measurements are preferred.

Result:500g flour ≈ 4 cups

Example 2: Travel Speed Conversion

Problem:A car is traveling at 120 km/h. What is that in mph?

Solution:Conversion factor: 1 km/h = 0.621371 mph 120 km/h × 0.621371 = 74.56 mph Alternatively: 120 ÷ 1.60934 = 74.56 mph

Result:120 km/h = 74.56 mph

Example 3: Real Estate Area

Problem:A property listing shows 2,000 square feet. What is that in square meters?

Solution:Conversion: 1 sq ft = 0.092903 sq m 2,000 sq ft × 0.092903 = 185.8 sq m Or: 2,000 ÷ 10.764 = 185.8 sq m This is equivalent to about 1.86 are or 0.0186 hectares.

Result:2,000 sq ft = 185.8 sq m

Frequently Asked Questions

How do I convert between different units?

Select the category (length, weight, temperature, etc.), enter your value, and choose the 'from' and 'to' units. The converter instantly shows the result. You can also see a complete conversion table showing your value in all units of that category.

What's the difference between US and UK gallons?

A US gallon is 3.785 liters, while a UK (Imperial) gallon is 4.546 liters. UK gallons are about 20% larger. This difference affects all derived units (quarts, pints) too. Always clarify which system when converting volumes.

How do I convert Celsius to Fahrenheit?

Formula: °F = (°C × 9/5) + 32. For example, 25°C = (25 × 1.8) + 32 = 77°F. Reverse: °C = (°F - 32) × 5/9. Key reference points: 0°C = 32°F (freezing), 100°C = 212°F (boiling), 37°C = 98.6°F (body temp).

What is Kelvin and when is it used?

Kelvin is the SI unit of temperature, used in science. It starts at absolute zero (-273.15°C), the coldest possible temperature. To convert: K = °C + 273.15. There are no negative Kelvin values. Room temperature (20°C) = 293.15K.

How many ounces are in a pound?

There are 16 ounces in 1 pound. To convert pounds to ounces, multiply by 16. To convert ounces to pounds, divide by 16. For example, 2.5 pounds = 40 ounces, and 24 ounces = 1.5 pounds.

What's the difference between mass and weight?

Mass measures the amount of matter (constant everywhere) in kilograms. Weight is the force of gravity on mass (varies by location) in Newtons. On Earth, we use them interchangeably, but in physics and space, they differ significantly.

How do I convert square feet to square meters?

1 square meter = 10.764 square feet. To convert sq ft to sq m, divide by 10.764. To convert sq m to sq ft, multiply by 10.764. For example, 100 sq ft = 9.29 sq m. Note: don't square the linear conversion factor.

What is a knot in speed measurement?

A knot is 1 nautical mile per hour, used in maritime and aviation. 1 knot = 1.852 km/h = 1.151 mph. The name comes from the old practice of measuring ship speed by counting knots on a rope paid out over time.

How accurate are these conversions?

Conversions use precise international standards and are accurate to 6 decimal places. For most practical purposes, 2-3 decimal places are sufficient. Scientific applications may require additional precision beyond what's displayed here.

When should I use metric vs imperial units?

Use metric for science, medicine, international communication, and precision work. Use imperial when required by local convention (US construction, cooking, road signs). Engineering increasingly uses metric. Always match the unit system expected by your audience or industry.

Background & Theory

Unit conversion is the process of expressing a quantity in different units while maintaining the same value. Understanding conversion fundamentals helps in science, engineering, cooking, travel, and daily life.

Metric (SI) System:

Based on powers of 10:

kilo- (k) = 1,000
hecto- (h) = 100
deka- (da) = 10
base unit = 1
deci- (d) = 0.1
centi- (c) = 0.01
milli- (m) = 0.001
micro- (μ) = 0.000001

Common Conversion Factors:

Length:

1 inch = 2.54 cm (exact)
1 foot = 30.48 cm
1 yard = 0.9144 m
1 mile = 1.60934 km

Weight:

1 ounce = 28.3495 g
1 pound = 453.592 g
1 kg = 2.20462 lb

Volume:

1 fluid oz = 29.5735 mL
1 cup = 236.588 mL
1 gallon (US) = 3.78541 L

Temperature Formulas:

°F = (°C × 9/5) + 32
°C = (°F - 32) × 5/9
K = °C + 273.15
°R = (°C + 273.15) × 9/5

Conversion Process:

Identify units: Source and target
Find conversion factor: Ratio between units
Multiply or divide: Depending on direction
Check reasonableness: Does answer make sense?

Dimensional Analysis:

Units can be treated algebraically:
5 km × (1000 m / 1 km) = 5000 m

The km units cancel, leaving meters.

Common Mistakes:

Squaring linear factors for area (wrong)
Cubing linear factors for volume (wrong)
Confusing mass and weight
Mixing US and UK gallons
Temperature: additive shift, not just ratio

Tips for Accuracy:

Use exact conversion factors when known
Carry extra decimal places during calculation
Round only the final answer
Double-check by converting back
Note which measurement system (US/UK/SI)

History

Unit systems have developed throughout human history, often based on human body measurements or natural phenomena. The Egyptian cubit (length of forearm) and the Roman foot (pes) are ancient examples still reflected in modern units. The metric system was born during the French Revolution (1790s), designed as a rational, decimal-based system. The meter was originally defined as one ten-millionth of the distance from the North Pole to the equator. The kilogram was defined by a platinum-iridium cylinder kept in Paris. The British Imperial system codified in 1824 formalized English units. The United States customary units diverged slightly from Imperial measures, creating the US/UK gallon distinction that persists today. In 1960, the International System of Units (SI) was established, modernizing and standardizing the metric system. The seven SI base units (meter, kilogram, second, ampere, kelvin, mole, candela) form the foundation of modern measurement. In 2019, all SI units were redefined based on fundamental physical constants rather than physical artifacts. The kilogram is now defined by the Planck constant, ensuring measurement standards that are universal, unchanging, and reproducible anywhere. Today, only three countries (US, Myanmar, Liberia) haven't officially adopted the metric system, though metric is used in science and international trade worldwide. Digital converters make translation between systems instantaneous.