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Tip: Use percent error when you have an accepted/true value. Use percent difference when you’re comparing two experimental values.

This only changes labels — the math stays the same.

This is the value you measured or calculated.

This is the reference / textbook / “true” value.

Units don’t affect percent calculations — we just display them.

Options:

Percent results are usually reported as positive (magnitude). Signed percent tells you if you’re above (+) or below (−).

This rounds the displayed results (helpful for lab reports). It won’t change your raw inputs.

Chips prefill a scenario and run the calculation.

Result:

No results yet. Enter values and click Calculate.

How to use this calculator

  • Choose percent error or percent difference.
  • Enter your two values (and optional units for display).
  • Optional: turn on signed percent and choose significant figures.
  • Click Calculate to see results, steps, and the mini visual.

How this calculator works

  • Difference: Δ = value₁ − value₂
  • Absolute difference: |Δ|
  • Percent error: (|Δ| / |accepted|) × 100
  • Percent difference: (|Δ| / ((|A|+|B|)/2)) × 100

Formula & Equation Used

Percent error: percent error = (|experimental − accepted| / |accepted|) × 100%

Percent difference: percent difference = (|A − B| / ((|A| + |B|)/2)) × 100%

Signed percent (optional): signed % = (Δ / baseline) × 100% For percent error baseline is accepted. For percent difference baseline is (|A|+|B|)/2.

Example Problem & Step-by-Step Solution

Example 1 — Percent error (gravity)

  1. Experimental: 9.81 m/s², Accepted: 9.80 m/s².
  2. Compute difference: Δ = 9.81 − 9.80 = 0.01.
  3. Percent error: ( |0.01| / |9.80| ) × 100 ≈ 0.102%.

Example 2 — Percent error (below accepted)

  1. Experimental: 9.72 m/s², Accepted: 9.80 m/s².
  2. Difference: Δ = 9.72 − 9.80 = −0.08.
  3. Percent error (magnitude): ( |−0.08| / |9.80| ) × 100 ≈ 0.816%.
  4. If you show signed percent: ( −0.08 / 9.80 ) × 100 ≈ −0.816% (below accepted).

Example 3 — Percent difference (two measurements)

  1. Two trials: A = 0.92 g/mL and B = 1.00 g/mL.
  2. Difference: |A − B| = |0.92 − 1.00| = 0.08.
  3. Average baseline: (|A|+|B|)/2 = (0.92 + 1.00)/2 = 0.96.
  4. Percent difference: (0.08 / 0.96) × 100 ≈ 8.33%.

Frequently Asked Questions

Q: Percent error vs percent difference — what’s the difference?

Use percent error when you have an accepted/true value. Use percent difference when comparing two measured values and neither is “the truth.”

Q: What if the accepted value is 0?

Percent error is undefined because it would divide by 0. You can still report the raw difference.

Q: Why are my results rounded?

If you choose significant figures, the calculator rounds the displayed results to match lab-report style.