Image Compression Calculator

Calculate image compression savings

Results

Calculated
Result
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What it is and when to use it

Image compression shrinks the file size of a picture so it uses less storage and loads faster. Lossy formats such as JPEG and WebP discard detail the eye is less likely to notice, and the quality setting controls how much is discarded. Lower quality gives smaller files but more visible artefacts, so the goal is the lowest setting that still looks acceptable.

Use this calculator for a quick planning estimate of how large an image, or a batch of images, will be after compression at a chosen quality, and how much space that saves. It is a simple rule-of-thumb model, not a simulation of a specific encoder: real results vary with image content, dimensions, format and software, so always check the actual exported file.

The estimate and its variables

The calculator uses compressed size = original size × (quality ÷ 100) × 0.3, then saved = original − compressed and percent saved = saved ÷ original × 100.

  • Original size: the uncompressed or source file size, in megabytes.
  • Quality %: the quality setting from 1 to 100, where a higher number means more detail retained.
  • 0.3: a fixed planning factor that assumes the output at 100% quality is about 30% of the source size.

Because the factor is fixed, the percentage saved depends only on quality: it equals 100 − 0.3 × quality, so 100% quality saves 70% and 50% quality saves 85%.

Worked example: a 5 MB photo at quality 80

Compressed size = 5 × 0.80 × 0.3 = 1.20 MB.

Saved = 5 − 1.20 = 3.80 MB, and the percentage saved is 3.80 / 5 × 100 = 76.0%. The result line reads Compressed: 1.20 MB | Saved: 3.80 MB (76.0%) | Quality: 80%.

If you compress 200 photos of this size at the same setting, the estimate scales to 240 MB instead of 1,000 MB. Test a few real files to check whether your images behave in the same way.

Common mistakes and how to interpret the result

  • Treating the estimate as exact. A busy photograph and a flat graphic compress very differently at the same quality number, so measure real output before committing to a setting.
  • Assuming quality numbers are comparable between tools. A quality of 80 in one editor is not the same as 80 in another, and formats such as JPEG, WebP and AVIF respond differently.
  • Re-compressing repeatedly. Every pass through a lossy encoder loses detail, so always start from the original file and export once.
  • Using lossy compression for the wrong content. Screenshots, text and sharp-edged graphics often look better and can be smaller as PNG, while photos suit lossy formats.

Frequently Asked Questions

What does the quality percentage mean?
It is the encoder's setting for how much detail to keep. Higher values keep more detail and give bigger files, while lower values discard more and can show blockiness or blur. The scale is not standardised between programs.
Why is 0.3 used in the formula?
It is a planning assumption that the compressed file at 100% quality is roughly 30% of the input size. Real ratios vary widely by format and content, which is why this is only an estimate.
What quality is a good starting point for the web?
Many people start around 75 to 85 for photographs and adjust by eye. Compare the result at normal viewing size, and reduce the setting until artefacts start to become visible.
Does compressing an image change its dimensions?
No. Compression changes how the pixel data is encoded, not how many pixels there are. To reduce file size further, you can also resize the image to the dimensions it is actually displayed at.

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Restaurant (sit-down)15–20%20%+ for exceptional service
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Hotel housekeeping$2–5/nightLeave daily, not just at checkout
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General Household Budget Ratios (50/30/20 Rule)

Category% of Net IncomeExamples
Needs50%Rent, groceries, utilities, insurance
Wants30%Dining out, entertainment, hobbies
Savings / Debt20%Emergency fund, retirement, extra payments

Common Measurement Conversions for Everyday Use

QuantityUS / ImperialMetric Equivalent
1 cup8 fl oz237 mL
1 pint16 fl oz473 mL
1 quart32 fl oz946 mL
1 gallon128 fl oz3.785 L
1 lb16 oz453.6 g
1 ft12 in30.48 cm

Practical Guide for Image Compression Calculator

Image Compression Calculator is most useful when the inputs reflect the situation you are actually planning around, not a best-case estimate. Treat the result as a decision aid: it gives you a structured way to compare assumptions, spot outliers, and decide what to verify next. For Specialized work, the most important review lens is definition consistency, measurement window, data quality, and whether the metric matches the decision being made.

Start with a baseline run using values you can defend. Then change one assumption at a time and watch which output moves the most. If one input dominates the result, spend your verification time there first. If several inputs have similar influence, use a conservative scenario and an optimistic scenario to create a practical range instead of relying on a single exact number.

Before acting on the result, compare the result with the source system or analytics export that produced the inputs. This is especially important when the calculator supports a purchase, project plan, performance target, or operational decision. The calculator can make the math consistent, but the quality of the conclusion still depends on current data, clear units, and assumptions that match your real constraints.

When the output looks surprising, slow down and inspect each input in order. A small change in one high-leverage field can move the final number more than several low-leverage fields combined. For Image Compression Calculator, that means you should first confirm the value with the greatest scale, then confirm the value with the greatest uncertainty, then rerun the calculator with conservative and optimistic assumptions. This sequence turns the calculator from a single answer into a practical decision range.

Review Checklist

  • Confirm every input uses the unit and time period requested by the calculator.
  • Run a low, expected, and high scenario so the answer has a useful range.
  • Check whether rounding or a missing decimal place changes the decision.
  • Update the calculation each reporting cycle or whenever tracking, attribution, pricing, or process rules change.

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