Thermometer Accuracy Checklist

Use this tool to verify your thermometer's accuracy, understand common error sources, and log comparison readings. Supports °C and °F. All calculations run offline in your browser.

Educational only, not medical advice.

Accuracy Check

Unit System

Your Thermometer Reading

Enter the temperature shown on your device

Reference Temperature

Known accurate value (e.g., calibrated thermometer, ice bath 0°C)

Measurement Site

Accuracy Results

Enter values to see analysis

Quick Accuracy Checklist

Device calibrated within last year Battery is fresh/adequate Properly positioned per manufacturer guide No drafts or extreme room temperature Waited required time after eating/drinking Sensor is clean and undamaged

0 of 6 checklist items marked

Why Thermometer Accuracy Matters

Small temperature differences can change medical decisions. A 0.5°C error might incorrectly suggest fever or mask an actual one. Regular accuracy checks help ensure your device provides reliable data for health monitoring.

Step-by-Step Guide

Find a reliable reference temperature (ice bath 0°C/32°F, boiling water 100°C/212°F at sea level, or a calibrated lab thermometer).
Measure the same temperature source with your device and the reference.
Enter both values in the calculator above.
Review the difference and percentage error.
Complete the checklist to identify common error sources.
If error exceeds manufacturer specs (typically ±0.1°C for clinical, ±0.3°C for consumer), consider calibration or replacement.

Example Checks

Scenario	Your Reading	Reference	Difference	Assessment
Ice bath test	0.2°C	0.0°C	+0.2°C	Minor error, typical for consumer devices
Oral check vs. calibrated	36.5°C	37.0°C	-0.5°C	Potentially significant; verify technique
Forehead vs. oral	98.2°F	98.6°F	-0.4°F	Normal site variation

Typical Accuracy Ranges

Thermometer Type	Typical Accuracy	When to Recalibrate/Replace
Clinical digital (oral/rectal)	±0.1°C (±0.2°F)	Error >0.2°C or after 2-3 years
Tympanic (ear)	±0.2°C (±0.4°F)	Error >0.3°C or inconsistent readings
Temporal (forehead)	±0.3°C (±0.5°F)	Error >0.5°C or after 1-2 years
Consumer digital	±0.3°C (±0.5°F)	Error >0.5°C or battery change

Measurement Site Adjustments

Different measurement sites show slightly different temperatures. Use this guide to compare readings across sites.

From Site Temperature at Above Site

To Site

Estimated Equivalent

Select sites and enter temperature

Note: Adjustments are approximate averages. Individual variation exists. When comparing devices, always measure the same site.

Frequently Asked Questions

How often should I check my thermometer's accuracy?

For home use, check every 6-12 months or if you suspect incorrect readings. Clinical settings may require monthly checks. Always verify after battery replacement or physical impact.

What's an acceptable error margin?

For fever detection, an error under 0.3°C (0.5°F) is generally acceptable. Clinical thermometers often specify ±0.1°C. Check your device's manual for manufacturer specifications.

Why does my thermometer show different values on repeat measurements?

Small variations are normal due to measurement technique, device warm-up, and body temperature fluctuations. Consistent differences >0.3°C suggest calibration issues.

When should I seek professional help?

If you experience symptoms like fever with chills, confusion, difficulty breathing, or severe pain—regardless of thermometer reading—seek medical attention. Don't rely solely on home devices.

Formulas & Assumptions

Difference = Thermometer Reading − Reference Temperature
Percentage Error = (Difference / Reference Temperature) × 100%
°F to °C: C = (F − 32) × 5/9
°C to °F: F = (C × 9/5) + 32
Site adjustments based on typical offsets: Rectal ≈ Oral +0.5°C, Axillary ≈ Oral −0.5°C, Tympanic ≈ Oral −0.3°C, Temporal ≈ Oral −0.3°C
All calculations round to 0.1°C or 0.1°F for display

Disclaimer: For informational and educational purposes only. Estimates depend on your inputs and simplifying assumptions. This tool is not medical advice and does not diagnose or treat any condition. If you have symptoms, abnormal readings, or urgent concerns, contact a qualified healthcare professional.

Sources & References:

Common unit conversions and measurement best practices
Typical wellness metric ranges and public health guidance concepts
Manufacturer accuracy specifications for common thermometer types
General measurement site variation guidance concepts

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Thermometer Accuracy Checklist

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