MYP Physics: Units & Significant Figures — The Complete FAQ

Because it's a habit, not a concept — students understand the physics but forget the presentation rules under time pressure. The MYP Sciences guide assesses this under Criterion B (Inquiring and Designing) and Criterion C (Processing and Evaluating), so a correct number with the wrong unit or sig figs still loses marks.

The most common mistake is giving a final answer to more significant figures than the data allows — for example, writing 4.836 m/s when the measurements only justify 4.8 m/s. Your answer can never be more precise than your least precise input measurement.

Because MYP Sciences criteria reward correct scientific communication, not just correct arithmetic. A right number with a missing unit, wrong unit, or an unjustified number of sig figs is treated as an incomplete answer under Criterion C strands about processing and interpreting data.

Match the significant figures in your final answer to the least precise piece of data given in the question — usually 2 or 3 sig figs in MYP problems. If the question doesn't specify, 3 significant figures is a safe, widely accepted default for most calculations.

Use the SI base or derived unit that matches the formula you're applying — speed is always metres per second (m/s), force is newtons (N), energy is joules (J). If a question gives data in different units (like km/h or grams), convert to SI units before you calculate, not after.

Round only at the final step, never mid-calculation, and count sig figs from the first non-zero digit. Leading zeros (0.0042) don't count; trailing zeros after a decimal point (4.20) do count. Keep at least one extra guard digit through your working and round only when you write the final answer.

Multiply or divide by the conversion factor, and always write the units alongside the numbers so they visibly cancel — this catches most errors before you finish the calculation. For example, converting 72 km/h to m/s: 72 × 1000 ÷ 3600 = 20 m/s.

Criteria B and C in MYP Sciences explicitly assess whether data and results are presented with correct units, appropriate precision, and clear labelling — not just whether the final number is right. Missing a unit on a table column or rounding inconsistently across a data set both cost marks under these strands.

Yes — MYP assessment criteria (particularly Criterion C strands on processing data) explicitly require correct units and appropriate significant figures as part of scientific communication. A numerically correct answer without units, or with the wrong unit, is marked as incomplete under the school's MYP-aligned assessment task.

Accuracy means how close a measurement is to the true value; precision means how consistent repeated measurements are with each other. Yes, it matters for marks — Criterion C often asks students to comment on both when evaluating experimental results, and confusing the two terms is a very common mistake.

The underlying rules don't change, but the stakes rise sharply in DP. According to the IB, first exams for the current DP Physics guide were 2025, and DP papers assess sig figs and units directly through markschemes with dedicated marks — MYP treats them as part of broader criteria strands instead.

The best practice is short, repeated drills rather than long study sessions — five quick conversion or rounding questions most days beats one long session before a test. Topical worksheets that isolate this single skill (rather than mixing it into full physics problems) help students build the habit before applying it under exam pressure.

Worked examples with visible step-by-step rounding, short topical worksheets focused only on units and sig figs, and past assessment tasks marked against the actual MYP criteria are the three most useful resource types — mixing all three beats relying on one alone.