Imperial to Metric Calculator

Q: How many centimeters are in a foot?

One foot is 30.48 centimeters . That is because a foot has 12 inches, and each inch is 2.54 cm. So 12 × 2.54 = 30.48. For a fast guess, think of 30 cm per foot. A 6 foot person is about 183 cm tall.

Q: Is a US gallon the same as a UK gallon?

No. They are different sizes. US gallon = 3.785 liters UK (imperial) gallon = 4.546 liters The UK gallon is about 20% bigger. This matters for fuel economy numbers. A car rated at 40 miles per UK gallon is only about 33 miles per US gallon.

Q: What is 1/2 inch in millimeters?

Half an inch is 12.7 mm . Here are other common ones: 1/8 in = 3.175 mm 1/4 in = 6.35 mm 3/8 in = 9.525 mm 3/4 in = 19.05 mm 1 in = 25.4 mm Turn the fraction into a decimal first, then multiply by 25.4.

Q: Does a metric ton weigh the same as a US ton?

No. A metric ton is 1,000 kg (about 2,205 lb). A US short ton is 2,000 lb (about 907 kg). The metric ton is about 10% heavier. A UK long ton is different again, at 2,240 lb. Always check which ton is meant on shipping or scrap papers.

Q: What is 32 psi in bar and kPa?

32 psi is about 2.2 bar or 221 kPa . To convert, multiply psi by 6.895 to get kPa, or by 0.0689 to get bar. Many tire gauges show both. Car tire pressure is usually 30 to 35 psi, which is about 2.1 to 2.4 bar.

Imperial to Metric Calculator

Introduction

This Imperial to Metric Calculator changes inches to centimeters, pounds to kilograms, gallons to liters, and much more. Pick a category, type a number, and read the answer.

It covers 10 kinds of measurements: length, weight, volume, area, temperature, speed, pressure, energy, power, and flow rate. The Swap button flips the conversion the other way, so metric to imperial works too.

For each answer you get the full math, step by step, so you can see how it works. A table shows your value in every unit in that group, and a chart compares the sizes. You choose how many decimal places you want, from 0 to 10.

Working with length? You can type fractions like 3/8 or 1 3/4 instead of decimals. That helps with tape measures, tools, and building plans.

Use it for cooking, school work, travel, shop projects, or any time you need to move between imperial and metric units.

How to use our Imperial to Metric Calculator

Pick what you are measuring, type your number, and choose your units. The calculator shows the metric (or imperial) answer, the steps, a full unit table, and a chart.

Measurement Category: Choose what you want to convert, like length, weight, volume, area, temperature, speed, pressure, energy, power, or flow rate. This loads the right units.

Value to Convert: Type the number you want to change. You can use decimals, and minus signs work for temperature.

Fractional Inches (optional): For length, you can type a fraction like 3/8 or a mixed number like 1 3/4. It updates the decimal value for you.

Decimal Places: Pick how many digits you want after the decimal point, from 0 to 10. Use more for exact work, less for quick math.

From Unit: Pick the unit your number is in now, such as inches, pounds, or gallons.

To Unit: Pick the unit you want the answer in, such as centimeters, kilograms, or liters.

Swap: Click this to flip the From and To units and convert the other way.

Calculate, Reset, and Copy result: Click Calculate to update the answer, Reset to start over with the default setup, or Copy result to copy the number.

Imperial to Metric Conversion

The world uses two main measuring systems. The imperial system (also called US customary) uses inches, feet, miles, pounds, gallons, and degrees Fahrenheit. The metric system (also called SI) uses meters, grams, liters, and degrees Celsius. Most countries use metric. The United States still uses imperial for daily life. Converting between them means changing a number from one system to the other without changing the real size of the thing you measured.

How Conversion Works

Every unit has a fixed size. To convert, you multiply or divide by a set number called a conversion factor. For example, 1 inch is always 2.54 centimeters. So 10 inches is 10 × 2.54 = 25.4 centimeters. The object did not change. Only the label and the number changed.

A simple trick: to go from a big unit to a small unit, you multiply and the number gets bigger. To go from a small unit to a big unit, you divide and the number gets smaller.

Common Conversion Factors

Length: 1 inch = 2.54 cm · 1 foot = 0.3048 m · 1 mile = 1.609 km
Weight: 1 ounce = 28.35 g · 1 pound = 0.4536 kg · 1 US ton = 907.18 kg
Volume: 1 fluid ounce = 29.57 mL · 1 US gallon = 3.785 L
Area: 1 square foot = 0.0929 m² · 1 acre = 0.4047 hectares
Speed: 1 mph = 1.609 km/h · 1 knot = 1.852 km/h
Pressure: 1 psi = 6.895 kPa
Power: 1 horsepower = 745.7 watts
Energy: 1 BTU = 1055 joules

Temperature Is Different

You cannot convert temperature with just one multiply. Fahrenheit and Celsius start at different zero points, so you also need to add or subtract. Use these formulas:

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

Water freezes at 32 °F, 0 °C, and 273.15 K. It boils at 212 °F, 100 °C, and 373.15 K.

Why It Matters

Recipes, tools, car parts, medicine doses, building plans, and school work often mix the two systems. A wrong conversion can ruin a cake, break a part, or cost a lot of money. In 1999 NASA lost a Mars spacecraft because one team used imperial units and another used metric. Careful conversion keeps work safe and correct.

Tips for Accurate Results

Check that both units measure the same thing. You cannot convert pounds into liters.
Watch out for US and UK gallons. A UK gallon is about 4.546 L, which is bigger than the US gallon.
Keep extra decimal places while you work, then round only at the end.
For inches, fractions like 3/8 or 1 3/4 are common. Turn them into decimals first (3 ÷ 8 = 0.375) before you multiply.

Formulas used

Convert value to base unit (factor-based)

V_{\text{base}} = V_{\text{from}} \times f_{\text{from}}

Convert base unit to target unit

V_{\text{to}} = \frac{V_{\text{base}}}{f_{\text{to}}}

Combined single-step conversion factor

V_{\text{to}} = V_{\text{from}} \times \frac{f_{\text{from}}}{f_{\text{to}}}

Fahrenheit to Kelvin (temperature to base)

K = (^\circ F - 32) \times \frac{5}{9} + 273.15

Celsius to Kelvin (temperature to base)

K = {^\circ C} + 273.15

Kelvin to Fahrenheit (base to temperature)

^\circ F = (K - 273.15) \times \frac{9}{5} + 32

Kelvin to Celsius (base to temperature)

^\circ C = K - 273.15

Decimal value to fraction (mixed number, denominator d)

V = \lfloor V \rfloor + \frac{\text{round}\big((V - \lfloor V \rfloor) \times d\big)}{d},\quad d = 64

Frequently asked questions

How many centimeters are in a foot?

One foot is 30.48 centimeters. That is because a foot has 12 inches, and each inch is 2.54 cm. So 12 × 2.54 = 30.48.

For a fast guess, think of 30 cm per foot. A 6 foot person is about 183 cm tall.

Is a US gallon the same as a UK gallon?

No. They are different sizes.

US gallon = 3.785 liters
UK (imperial) gallon = 4.546 liters

The UK gallon is about 20% bigger. This matters for fuel economy numbers. A car rated at 40 miles per UK gallon is only about 33 miles per US gallon.

What is a quick way to convert Fahrenheit to Celsius in your head?

Subtract 30, then cut the answer in half. For 70 °F: 70 − 30 = 40, then 40 ÷ 2 = 20 °C. The exact answer is 21.1 °C, so you are close.

To go back, double the Celsius number and add 30. Use the full formula when you need to be exact.

How do you convert mph to km/h quickly?

Multiply by 1.6. So 60 mph is about 96 km/h, and 30 mph is about 48 km/h.

The exact factor is 1.609344. Going the other way, multiply km/h by 0.62. A 100 km/h speed limit is about 62 mph.

What is 1/2 inch in millimeters?

Half an inch is 12.7 mm. Here are other common ones:

1/8 in = 3.175 mm
1/4 in = 6.35 mm
3/8 in = 9.525 mm
3/4 in = 19.05 mm
1 in = 25.4 mm

Turn the fraction into a decimal first, then multiply by 25.4.

Why is an inch exactly 2.54 centimeters?

It was agreed on. In 1959, the US, UK, and other countries signed the international yard and pound agreement. They set one yard at exactly 0.9144 meters.

That makes one inch exactly 0.0254 meters, or 2.54 cm. It is a definition, not a rounded number, so it never changes.

How do you convert square feet to square meters?

Divide square feet by 10.764, or multiply by 0.0929. A 1,000 sq ft home is about 92.9 m².

Area factors are the length factor squared. Since 1 ft = 0.3048 m, then 0.3048 × 0.3048 = 0.09290. Never use the plain length factor for area.

Why can't you convert temperature with just one multiplication?

Because the scales start at different zeros. Zero °C is the freezing point of water, but zero °F is much colder, and zero K is absolute zero.

So you must shift the number and scale it. That is why the formula has both a multiply and an add or subtract: °C = (°F − 32) × 5/9.

Does a metric ton weigh the same as a US ton?

No. A metric ton is 1,000 kg (about 2,205 lb). A US short ton is 2,000 lb (about 907 kg).

The metric ton is about 10% heavier. A UK long ton is different again, at 2,240 lb. Always check which ton is meant on shipping or scrap papers.

What is 32 psi in bar and kPa?

32 psi is about 2.2 bar or 221 kPa.

To convert, multiply psi by 6.895 to get kPa, or by 0.0689 to get bar. Many tire gauges show both. Car tire pressure is usually 30 to 35 psi, which is about 2.1 to 2.4 bar.

How many kilowatts is one horsepower?

One mechanical horsepower is 745.7 watts, or about 0.746 kW.

So a 200 hp car engine makes about 149 kW. To go the other way, multiply kW by 1.341. A 100 kW motor is about 134 hp.

How many milliliters are in a cup for baking?

A US cup is 236.6 mL, usually rounded to 240 mL in recipes. Other handy ones:

1 tablespoon = 14.8 mL
1 fluid ounce = 29.6 mL
1 pint = 473 mL
1 quart = 946 mL

A metric cup used in Australia is 250 mL, so recipes can differ.

Which countries still use the imperial system?

Only three countries have not officially adopted metric: the United States, Liberia, and Myanmar.

The UK and Canada are mostly metric but still use imperial for some things, like miles for road signs in the UK and pounds for body weight.

How fast is one knot in mph and km/h?

One knot equals 1.151 mph or 1.852 km/h.

A knot is one nautical mile per hour. A nautical mile is based on the size of the Earth, which is why ships and planes use it for navigation.

How many BTU are in a kilowatt-hour?

One kilowatt-hour equals about 3,412 BTU.

Air conditioners and heaters are often rated in BTU per hour. A 12,000 BTU/h unit uses about 3.5 kW of heat energy, which is also called one ton of cooling.

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