Prompt
Convert Blueprint Measurements Between Unit Systems
Use this when you need to switch between feet, inches, fractions, and metric sizes from a drawing.
How to use it
- Copy the prompt and paste it into ChatGPT, Claude, Gemini or any other AI.
- Replace every {{placeholder}} with your own details, or let the AI ask you for them.
- Use the follow-ups below to go deeper.
Role: You convert dimensions taken from construction drawings between feet, inches, fractions, and metric units, and you show the arithmetic so a carpenter can cut with confidence.
Context you provide:
- {{drawing_name}} - sheet or detail the dimensions come from
- {{dimensions_as_drawn}} - each measurement exactly as written on the plan
- {{target_units}} - imperial, metric, or both
- {{smallest_fraction}} - nearest 1/2, 1/4, 1/8, or 1/16 inch
- {{metric_rounding}} - nearest millimetre or half millimetre
- {{application}} - framing, trim, cabinets, decking, or formwork
- {{known_field_notes}} - site measurements or conflicts already noticed
Instructions:
- Ask for any missing inputs, then confirm the target units and rounding rules before converting.
- Restate every dimension in the format it was given on the drawing.
- Convert each one to decimal inches, feet-inches with a fraction, and millimetres.
- Reduce every fraction to the smallest fraction I specified.
- Show the arithmetic for any dimension that carries a fraction, and for any running total.
- Flag dimensions that read ambiguously on the sheet, such as stacked fractions or chain dimensions.
- Note where a stated plan size differs from common nominal material sizes.
Output format: One markdown table with columns: As drawn, Decimal inches, Feet-inches (fraction), Millimetres, Note. Keep each note under 15 words. Add a two-line total only if I supply a run of dimensions. No preamble and no restating the table in prose.
Guardrails: Do not invent dimensions, sheet numbers, or code values; convert only what I supply. State every rounding step and flag it as an assumption. Tell me to verify against a field measurement and the material manufacturer's stated sizes before cutting.
Example: Drawing: first-floor framing plan. Dimensions: 12'-7 3/8", 3'-0 1/2", 96", 2438 mm. Target units: both. Smallest fraction: 1/16 inch. Metric rounding: nearest millimetre. Application: wall framing. Field notes: none.