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1.15 Ratios & Percentages

RATIOS

A ratio is a proportional relationship of one value to another, e.g., the ratio of gas to oil in chain saw mix. Ratios can be written either as a fraction, 1/2, or in ratio notation, 1:2. The value of a ratio is the division of the first number by the second number. For example, consider the ratio 1:40 . This ratio is read as "1 to 40". Any fraction, for instance, 1/20, can also be written as a ratio: 1:20

Example 1 - The Mara Bella District has 6 engines. The Baldy District has 5 engines. What is the ratio of engines in the Mara Bella versus the Baldy districts? 

The ratio of engines in the Mara Bella versus Baldy districts is 6:5 or 6/5.
 

PERCENTAGES

A percentage is another way of describing a ratio with respect to 100. Percent (%) is a value corresponding to how many out of a hundred (per hundred). For instance, if 92 out of 100 firefighters have completed the FireFighter Math course, the ratio of firefighters completing the course is 92:100, and the percentage is written as 92%.

Example 2 - Write four notations for 56.8%.

56.8% = 56.8 out of 100
56.8% = 56.8/100
56.8% = 56.8:100
56.8% = 0.568 (Note that performing this calculation results in moving the decimal two places to the left because there are two zeros in 100.)
 

PERCENTAGES AND LIVE FUEL MOISTURES

Percentages are useful for a number of fire science applications. One of these applications is estimating live fuel moisture. Live fuel moisture can be measured using oven drying and weighing procedures. Because this process is time-consuming and cannot be completed in the field, fire considerations are usually satisfied with a good estimate. Live fuel moisture can be estimated using the values in the figure below, which provides moisture percentages for fuels at different stages of vegetative development. For instance, from the figure, we observe that completely cured fuels have a live fuel moisture of less than 30%. This value is the result of subtracting the dry weight of the fuel from the total (wet) weight and dividing by the dry weight. 

Live Fuel Moisture %
 

Example 3 - A fuel sample collected in the field weighs 377 grams. After the sample is dried in an oven, it weighs 198 grams. What is the live fuel moisture content?

Step 1. Subtract the dry weight from the wet weight. 377 - 198 = 179.

Step 2.Divide the difference by the dry weight and multiply by 100 to find the value as a percent. 179 / 198 × 100 = 0.904 × 100 = 90.4%. 

The live fuel moisture of your sample is 90.4%. 
 

PROBLEM SOLVING WITH RATIOS

When solving a more complex percentage or ratio problem, write the problem down in words and numbers and work through one step at a time.

 

NWCG Latest Announcements

Updated NWCG Standards for Airtanker Base Operations, PMS 508

Date: March 31, 2025
Questions?  Please contact:
Airtanker Base Operations Unit

The updated NWCG Standards for Airtanker Base Operations (SABO), PMS 508 standardizes operations and procedures at interagency airtanker bases to ensure safe, efficient, and effective operations in support of interagency goals and objectives.

References:

NWCG Standards for Airtanker Base Operations, PMS 508

WFSTAR 2025 Core Component Module Package and 2024 Fire Year in Review Now Available

Date: March 14, 2025
Questions?  Please contact:
Joe Schindel at mschindel@blm.gov
 

The 2025 Core Component Module Package for RT-130, Wildland Fire Safety Training Annual Refresher (WFSTAR) and the 2024 Fire Year in Review are now available on the NWCG website. The 2025 Core Component Module Package provides all content needed to deliver RT-130.

References:

2025 Core Component Module Package

2024 Fire Year in Review Module

NEW! NWCG Wildland Urban Interface Mitigation Field Guide, PMS 053

Date: March 12, 2025
Contact: Wildland Urban Interface Mitigation Committee

The NWCG Wildland Urban Interface Mitigation Field Guide, PMS 053 provides mitigation practitioners at all experience levels with recommendations on the most effective and efficient ways to accomplish mitigation work in communities at risk to wildfire damage or destruction. The content in this guide was written in coordination with the NWCG Standards for Mitigation in the Wildland Urban Interface, PMS 052.

References:

NWCG Wildland Urban Interface Mitigation Field Guide, PMS 053 

Updated, NWCG Standards for Wildland Fire Module Operations, PMS 430

Date: March 11, 2025
Contact: Fire Use Subcommittee
Wildland Fire Module Unit

The NWCG Standards for Wildland Fire Module Operations, PMS 430 standardizes procedures and expectations for Wildland Fire Modules (WFMs). These standards are to be used by staff, supervisors, specialists, and technicians for planning, administering, and conducting WFM operations. These standards will also be used as a measure of WFM qualifications, capabilities, and expected performance, for both Type 1 and Type 2 WFMs.

References:

NWCG Standards for Wildland Fire Module Operations, PMS 430