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Body Surface Area (BSA) & Chemo Dosing Practice

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Many chemotherapy and some pediatric drugs are dosed per square meter of body surface area (BSA). The Mosteller formula is the simplest of the standard methods and the one exams use. Keep BSA unrounded until the final multiplication to avoid dosing errors.

FormulaBSA (m²) = √(height[cm] × weight[kg] ÷ 3600)  •  dose = mg/m² × BSA
Worked example

A patient is 170 cm and 70 kg. BSA = √(170 × 70 ÷ 3,600) = √3.306 = 1.82 m². A 175 mg/m² order → 175 × 1.82 = 318.5 mg.

Rounding trap: rounding BSA to one decimal too early can shift the dose by several mg, so carry full precision to the end.

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BSA Dosing
A patient is 160 cm tall and weighs 64 kg. The order is paclitaxel 175 mg/m². Using the Mosteller formula, what dose in mg should be prepared? Round your answer to the nearest whole number.
mg

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How to set up a body surface area dose

Chemotherapy and a handful of other drugs are dosed per square metre of body surface area rather than per kilogram, because for those drugs surface area tracks clearance better than weight does. The calculation has two parts, BSA and then dose, and the second part is trivial. The points are lost in the first part, and specifically in how much precision you carry through it.

Mosteller: BSA (m²) = √(height in cm × weight in kg ÷ 3,600)   •   dose = mg/m² × BSA

Mosteller is the formula exams use because it can be done on a basic calculator. Other formulas (DuBois, Haycock) give slightly different numbers; if a question names one, use that one, but if it just says "calculate the BSA" it means Mosteller.

Worked example

A patient is 165 cm tall and weighs 68 kg. The order is paclitaxel 175 mg/m².

height × weight = 165 × 68 = 11,220

11,220 ÷ 3,600 = 3.11667

BSA = √3.11667 = 1.76541 m²

dose = 175 × 1.76541 = 308.95 → 309 mg

Now do it again with the BSA rounded to 1.8 m², which is what a hurried student writes down: 175 × 1.8 = 315 mg. That's 6 mg over, about 2% of the dose, and on a narrow-therapeutic-index drug that's the difference between a graded-correct answer and a wrong one. Rounding to 1.77 gives 310 mg, still not 309. Keep every decimal the calculator shows until the final multiplication, and round once, at the end.

Units in, units out

Mosteller needs centimetres and kilograms. If the height is in inches, multiply by 2.54. If the weight is in pounds, divide by 2.2. Do the conversions first and write the converted figures down before touching the square root. A height of 65 inches put in as 65 cm gives a BSA of about 1.1 m² for an adult, which should look wrong immediately: adult BSAs run from roughly 1.5 to 2.2 m².

Total dose for a cycle

Some questions go one step further: the drug is given daily for several days, or the order is per cycle. Multiply the single dose by the number of doses after you have the single dose, not before. A drug given on day 1 of each cycle is one dose per cycle; a drug given daily for 3 days is three. The stem tells you which.

Where students lose the points

10 Body Surface Area (BSA) & Chemo Dosing practice problems with worked solutions

Every problem below is worked start to finish. Try it yourself first, then check the steps. For a fresh problem every time, use the practice box above. It generates unlimited variations of these same question types.

Problem 1: BSA Dosing

A patient is 170 cm tall and weighs 77 kg. The order is doxorubicin 60 mg/m². Using the Mosteller formula, what dose in mg should be prepared? Round your answer to the nearest whole number.

Answer 114 mg

Solution
  1. Mosteller: BSA = √(ht[cm] × wt[kg] ÷ 3600).
  2. 170 cm × 77 kg = 13090 cm·kg; 13090 ÷ 3,600 ≈ 3.63611.
  3. BSA = √3.63611 ≈ 1.90686 m².
  4. Dose = 60 mg/m² × 1.90686 m² ≈ 114 mg.
  5. Rounded as the question asks: 114 mg.

Keep BSA unrounded until the final multiplication. Round it to 2 decimals early and the dose can move by several mg, which is why the steps above carry 5.

Problem 2: BSA Dosing

A patient is 190 cm tall and weighs 83 kg. The order is gemcitabine 1000 mg/m². Using the Mosteller formula, what dose in mg should be prepared? Round your answer to the nearest whole number.

Answer 2,093 mg

Solution
  1. Mosteller: BSA = √(ht[cm] × wt[kg] ÷ 3600).
  2. 190 cm × 83 kg = 15770 cm·kg; 15770 ÷ 3,600 ≈ 4.38056.
  3. BSA = √4.38056 ≈ 2.09298 m².
  4. Dose = 1000 mg/m² × 2.09298 m² ≈ 2093 mg.
  5. Rounded as the question asks: 2,093 mg.

Keep BSA unrounded until the final multiplication. Round it to 2 decimals early and the dose can move by several mg, which is why the steps above carry 5.

Problem 3: BSA Dosing

A patient is 170 cm tall and weighs 70 kg. The order is cyclophosphamide 600 mg/m². Using the Mosteller formula, what dose in mg should be prepared? Round your answer to the nearest whole number.

Answer 1,091 mg

Solution
  1. Mosteller: BSA = √(ht[cm] × wt[kg] ÷ 3600).
  2. 170 cm × 70 kg = 11900 cm·kg; 11900 ÷ 3,600 ≈ 3.30556.
  3. BSA = √3.30556 ≈ 1.81812 m².
  4. Dose = 600 mg/m² × 1.81812 m² ≈ 1091 mg.
  5. Rounded as the question asks: 1,091 mg.

Keep BSA unrounded until the final multiplication. Round it to 2 decimals early and the dose can move by several mg, which is why the steps above carry 5.

Problem 4: BSA Dosing

A patient is 150 cm tall and weighs 62 kg. The order is etoposide 100 mg/m². Using the Mosteller formula, what dose in mg should be prepared? Round your answer to the nearest whole number.

Answer 161 mg

Solution
  1. Mosteller: BSA = √(ht[cm] × wt[kg] ÷ 3600).
  2. 150 cm × 62 kg = 9300 cm·kg; 9300 ÷ 3,600 ≈ 2.58333.
  3. BSA = √2.58333 ≈ 1.60727 m².
  4. Dose = 100 mg/m² × 1.60727 m² ≈ 161 mg.
  5. Rounded as the question asks: 161 mg.

Keep BSA unrounded until the final multiplication. Round it to 2 decimals early and the dose can move by several mg, which is why the steps above carry 5.

Problem 5: BSA Dosing

A patient is 175 cm tall and weighs 72 kg. The order is cyclophosphamide 600 mg/m². Using the Mosteller formula, what dose in mg should be prepared? Round your answer to the nearest whole number.

Answer 1,122 mg

Solution
  1. Mosteller: BSA = √(ht[cm] × wt[kg] ÷ 3600).
  2. 175 cm × 72 kg = 12600 cm·kg; 12600 ÷ 3,600 = 3.5.
  3. BSA = √3.5 ≈ 1.87083 m².
  4. Dose = 600 mg/m² × 1.87083 m² ≈ 1122 mg.
  5. Rounded as the question asks: 1,122 mg.

Keep BSA unrounded until the final multiplication. Round it to 2 decimals early and the dose can move by several mg, which is why the steps above carry 5.

Problem 6: BSA Dosing

A patient is 165 cm tall and weighs 53 kg. The order is irinotecan 180 mg/m². Using the Mosteller formula, what dose in mg should be prepared? Round your answer to the nearest whole number.

Answer 281 mg

Solution
  1. Mosteller: BSA = √(ht[cm] × wt[kg] ÷ 3600).
  2. 165 cm × 53 kg = 8745 cm·kg; 8745 ÷ 3,600 ≈ 2.42917.
  3. BSA = √2.42917 ≈ 1.55858 m².
  4. Dose = 180 mg/m² × 1.55858 m² ≈ 281 mg.
  5. Rounded as the question asks: 281 mg.

Keep BSA unrounded until the final multiplication. Round it to 2 decimals early and the dose can move by several mg, which is why the steps above carry 5.

Problem 7: BSA Dosing

A patient is 155 cm tall and weighs 59 kg. The order is paclitaxel 175 mg/m². Using the Mosteller formula, what dose in mg should be prepared? Round your answer to the nearest whole number.

Answer 279 mg

Solution
  1. Mosteller: BSA = √(ht[cm] × wt[kg] ÷ 3600).
  2. 155 cm × 59 kg = 9145 cm·kg; 9145 ÷ 3,600 ≈ 2.54028.
  3. BSA = √2.54028 ≈ 1.59383 m².
  4. Dose = 175 mg/m² × 1.59383 m² ≈ 279 mg.
  5. Rounded as the question asks: 279 mg.

Keep BSA unrounded until the final multiplication. Round it to 2 decimals early and the dose can move by several mg, which is why the steps above carry 5.

Problem 8: BSA Dosing

A patient is 150 cm tall and weighs 55 kg. The order is docetaxel 75 mg/m². Using the Mosteller formula, what dose in mg should be prepared? Round your answer to the nearest whole number.

Answer 114 mg

Solution
  1. Mosteller: BSA = √(ht[cm] × wt[kg] ÷ 3600).
  2. 150 cm × 55 kg = 8250 cm·kg; 8250 ÷ 3,600 ≈ 2.29167.
  3. BSA = √2.29167 ≈ 1.51383 m².
  4. Dose = 75 mg/m² × 1.51383 m² ≈ 114 mg.
  5. Rounded as the question asks: 114 mg.

Keep BSA unrounded until the final multiplication. Round it to 2 decimals early and the dose can move by several mg, which is why the steps above carry 5.

Problem 9: BSA Dosing

A patient is 165 cm tall and weighs 60 kg. The order is etoposide 100 mg/m². Using the Mosteller formula, what dose in mg should be prepared? Round your answer to the nearest whole number.

Answer 166 mg

Solution
  1. Mosteller: BSA = √(ht[cm] × wt[kg] ÷ 3600).
  2. 165 cm × 60 kg = 9900 cm·kg; 9900 ÷ 3,600 = 2.75.
  3. BSA = √2.75 ≈ 1.65831 m².
  4. Dose = 100 mg/m² × 1.65831 m² ≈ 166 mg.
  5. Rounded as the question asks: 166 mg.

Keep BSA unrounded until the final multiplication. Round it to 2 decimals early and the dose can move by several mg, which is why the steps above carry 5.

Problem 10: BSA Dosing

A patient is 155 cm tall and weighs 63 kg. The order is docetaxel 75 mg/m². Using the Mosteller formula, what dose in mg should be prepared? Round your answer to the nearest whole number.

Answer 124 mg

Solution
  1. Mosteller: BSA = √(ht[cm] × wt[kg] ÷ 3600).
  2. 155 cm × 63 kg = 9765 cm·kg; 9765 ÷ 3,600 = 2.7125.
  3. BSA = √2.7125 ≈ 1.64697 m².
  4. Dose = 75 mg/m² × 1.64697 m² ≈ 124 mg.
  5. Rounded as the question asks: 124 mg.

Keep BSA unrounded until the final multiplication. Round it to 2 decimals early and the dose can move by several mg, which is why the steps above carry 5.

Sources and how far they go

Where a convention on this page comes from a published standard, the standard is named. Where it comes from a textbook or from ordinary practice instead, the entry says so. That difference matters when a preceptor or an exam disagrees with you.

Citations are to the source of the method. They are not a review of this page, and none of these bodies has reviewed or endorsed it.

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