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Weight calculator

GCSEA-level Forces

Weight is the force of gravity on a mass, found from mass and gravitational field strength.

W = m g

This free calculator is for GCSE and A-level physics. Choose the quantity you want to find, enter the other values with their units, and it shows the working in the layout used in exams, with the answer to the number of significant figures you choose. The values shown are an example. Change them to your own.

Quantity to find

637 N

Working

  1. Write the equation
    W = m g
  2. Constants used
    g = 9.8 N/kg
  3. Substitute the values
    W = 65 × 9.8
  4. Calculate
    W = 637 N
  5. Give the answer to 3 significant figures
    W = 637 N

Worked example

Find W, the weight. Given: mass m = 65.0 kg; gravitational field strength g = 9.8 N/kg.

  1. Write the equation
    W = m g
  2. Constants used
    g = 9.8 N/kg
  3. Substitute the values
    W = 65 × 9.8
  4. Calculate
    W = 637 N
  5. Give the answer to 3 significant figures
    W = 637 N

Symbols and units

SymbolQuantitySI unit
WWeightN
mMasskg
gGravitational field strength (constant)N/kg

Weight: rearranged

  • To find weight: W = m g
  • To find mass: m = W / g

Exam tip

Mass is measured in kg and weight in N. Use the value of g given in your question, usually 9.8 or 9.81 N/kg on Earth.

Common questions

What is the formula for weight?

The equation is W = m g, where W is the weight (N); m is the mass (kg); g is the gravitational field strength (N/kg).

What units should I use for weight?

In SI units: weight in N, mass in kg, gravitational field strength in N/kg. The calculator also accepts common alternatives such as kilometres, grams or minutes, and converts them for you.

How do I rearrange W = m g?

Rearranging gives these forms: to find weight: W = m g. to find mass: m = W / g.

Practise weight questions

Press the button for a question with random numbers. Work it out on paper first, then type your answer.

Related

Read the full explanation on the Weight formula page. More forces equations: Newton’s second law, Moment of a force, Hooke’s law, Pressure, Pressure in a liquid, Density, Horizontal component of a force, Vertical component of a force. See the full list on the physics equation calculator page.